[Task] Make command copyable in README

## What should be done 
Make readme proper
To make it from this
```
cargo install lenra_cli --version=1.0.0-beta.5
# or `cargo install lenra_cli@1.0.0-beta.5`
```
to this
```
cargo install lenra_cli --version=1.0.0-beta.5
```
or 
```
cargo install lenra_cli@1.0.0-beta.5`
```
As it makes it time consuming.
Also a `hacktoberfest` label would be of help.

