Add missing links for TryFrom docs

[GuillaumeGomez]

r? @rust-lang/docs

[rust-highfive]

The job x86_64-gnu-llvm-6.0 of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

travis_time:end:014c790e:start=1561582960022547486,finish=1561582960777692844,duration=755145358
$ git checkout -qf FETCH_HEAD
travis_fold:end:git.checkout
Encrypted environment variables have been removed for security reasons.
See https://docs.travis-ci.com/user/pull-requests/#pull-requests-and-security-restrictions
$ export SCCACHE_BUCKET=rust-lang-ci-sccache2
$ export SCCACHE_REGION=us-west-1
$ export GCP_CACHE_BUCKET=rust-lang-ci-cache
$ export AWS_ACCESS_KEY_ID=AKIA46X5W6CZEJZ6XT55
---
travis_time:start:test_assembly
Check compiletest suite=assembly mode=assembly (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
[01:06:31] [01:06:31] running 9 tests
[01:06:31] iiiiiiiii
[01:06:31] [01:06:31] finished in 0.151
[01:06:31] travis_fold:end:test_assembly
---
travis_time:start:test_debuginfo
Check compiletest suite=debuginfo mode=debuginfo-gdb+lldb (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
[01:06:47] [01:06:47] running 122 tests
[01:07:12] .iiiii...i.....i..i...i..i.i.i..i.ii..i.i.....i..i....i..........iiii..........i...ii...i.......ii.i 100/122
[01:07:17] .i.i......iii.i.....ii
[01:07:17] [01:07:17] finished in 29.723
[01:07:17] travis_fold:end:test_debuginfo
---
[01:39:24] Checking compiler_builtins v0.1.16
[01:39:25] Documenting alloc v0.0.0 (/checkout/src/liballoc)
[01:39:29] Finished release [optimized] target(s) in 34.64s
[01:39:30] Documenting core v0.0.0 (/checkout/src/libcore)
[01:39:45] error: `[i32::MAX]` cannot be resolved, ignoring it...
[01:39:45] |
[01:39:45] |
[01:39:45] 417 | /// giving the [`i64`]'s value modulo [`i32::MAX`]) or by simply returning
[01:39:45] |
[01:39:45] note: lint level defined here
[01:39:45] --> src/libcore/lib.rs:64:9
[01:39:45] |
[01:39:45] |
[01:39:45] 64 | #![deny(intra_doc_link_resolution_failure)] // rustdoc is run without -D warnings
[01:39:45] | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[01:39:45] = help: to escape `[` and `]` characters, just add '\' before them like `\[` or `\]`
[01:39:45] [01:39:45] error: `[i32::MAX]` cannot be resolved, ignoring it...
[01:39:45] |
[01:39:45] |
[01:39:45] 418 | /// [`i32::MAX`], or by some other method. The [`From`] trait is intended
[01:39:45] |
[01:39:45] = help: to escape `[` and `]` characters, just add '\' before them like `\[` or `\]`
[01:39:45] [01:39:45] error: `[]` cannot be resolved, ignoring it...
[01:39:45] error: `[]` cannot be resolved, ignoring it...
[01:39:45] --> src/libcore/convert.rs:429:15
[01:39:45] |
[01:39:45] 429 | /// When the [`!`] type is stablized [`Infallible`] and [`!`] will be
[01:39:45] |
[01:39:45] = help: to escape `[` and `]` characters, just add '\' before them like `\[` or `\]`
[01:39:45] [01:39:45] error: `[]` cannot be resolved, ignoring it...
[01:39:45] error: `[]` cannot be resolved, ignoring it...
[01:39:45] --> src/libcore/convert.rs:429:58
[01:39:45] |
[01:39:45] 429 | /// When the [`!`] type is stablized [`Infallible`] and [`!`] will be
[01:39:45] |
[01:39:45] = help: to escape `[` and `]` characters, just add '\' before them like `\[` or `\]`
[01:39:45] [01:39:46] error: aborting due to 4 previous errors
[01:39:46] error: aborting due to 4 previous errors
[01:39:46] [01:39:46] error: Could not document `core`.
[01:39:46] [01:39:46] Caused by:
[01:39:46] process didn't exit successfully: `/checkout/obj/build/bootstrap/debug/rustdoc --edition=2018 --crate-name core src/libcore/lib.rs --color always --target x86_64-unknown-linux-gnu -o /checkout/obj/build/x86_64-unknown-linux-gnu/stage1-std/x86_64-unknown-linux-gnu/doc --markdown-css rust.css --markdown-no-toc --generate-redirect-pages --resource-suffix 1.37.0 --index-page /checkout/src/doc/index.md -L dependency=/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-std/x86_64-unknown-linux-gnu/release/deps -L dependency=/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-std/release/deps` (exit code: 1)
[01:39:46] [01:39:46] [01:39:46] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "rustdoc" "--target" "x86_64-unknown-linux-gnu" "-j" "4" "--release" "--locked" "--color" "always" "--features" "panic-unwind backtrace compiler-builtins-c" "--manifest-path" "/checkout/src/libstd/Cargo.toml" "-Z" "unstable-options" "-p" "core" "--" "--markdown-css" "rust.css" "--markdown-no-toc" "--generate-redirect-pages" "--resource-suffix" "1.37.0" "--index-page" "/checkout/src/doc/index.md"
[01:39:46] [01:39:46] [01:39:46] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
[01:39:46] Build completed unsuccessfully in 1:34:56
---
$ find $HOME/Library/Logs/DiagnosticReports -type f -name '*.crash' -not -name '*.stage2-*.crash' -not -name 'com.apple.CoreSimulator.CoreSimulatorService-*.crash' -exec printf travis_time:end:252a12f8:start=1561588959415059357,finish=1561588959483785904,duration=68726547
travis_fold:end:after_failure.4
travis_fold:start:after_failure.5
travis_time:start:2eda56d4
$ cat ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers || true
cat: ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers: No such file or directory
travis_fold:end:after_failure.5
travis_fold:start:after_failure.6
travis_time:start:000c795c
$ dmesg | grep -i kill

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[GuillaumeGomez]

Considering it's just adding links and no one emitted complains, I'll just r+ it I guess...

@bors: r=docs rollup

[bors]

📌 Commit dfb9f5b has been approved by docs