Infra: make htmllive: open browser when ready

[hugovk]

Like python/devguide#1233.

When running make htmllive, this will open the browser when the docs have been built the first time.

It means you don't need to hunt around for the link in:

❯ make htmllivevenv already exists.To recreate it, remove it first with `make clean-venv'..venv/bin/sphinx-autobuild -b html -j 8 --re-ignore="/\.idea/|/venv/|/pep-0000.rst|/topic/" --open-browser --delay 0 peps build[sphinx-autobuild] > sphinx-build -b html -j 8 /Users/hugo/github/peps/peps /Users/hugo/github/peps/buildRunning Sphinx v7.2.6loading pickled environment... donebuilding [html]: targets for 1 source files that are out of dateupdating environment: 0 added, 2 changed, 5 removedreading sources... [100%] topic/typinglooking for now-outdated files... none foundpickling environment... donechecking consistency... donepreparing documents... donecopying assets... copying static files... donecopying extra files... donedonewriting output... [100%] topic/typinggenerating indices... donewriting additional pages... donedumping object inventory... donebuild succeeded.The HTML pages are in build.[I 231130 18:08:54 server:335] Serving on http://127.0.0.1:8000[I 231130 18:08:54 handlers:62] Start watching changes[I 231130 18:08:54 handlers:64] Start detecting changes[I 231130 18:08:54 handlers:135] Browser Connected: http://127.0.0.1:8000/[I 231130 18:08:55 handlers:82] Ignore: /Users/hugo/github/peps/peps/pep-0418/clockutils.py[I 231130 18:08:56 handlers:92] Reload 1 waiters: None[I 231130 18:08:57 handlers:135] Browser Connected: http://127.0.0.1:8000/

I'll make the same changes for the CPython repo afterwards.

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📚 Documentation preview 📚: https://pep-previews--3558.org.readthedocs.build/

[JacobCoffee]

I added this for some of my projects after finding it. It's great.