According to the docs of this repo, so the example should not show it

pip's documentation explicitly states to not use `import pip`:

> While it is implemented in Python, and so is available from your Python code via
> `import pip`, you must not use pip’s internal APIs in this way.

This example is in direct contradiction with the documentation's guidance and, thus, has
been removed.

Also cache _build for Elixir

Extend gradle notes.

This commit applies the suggestion from The Cargo Book:
https://doc.rust-lang.org/cargo/guide/cargo-home.html#caching-the-cargo-home-in-ci

…or (#596)