Rename sub menu label containing docs.rs information "docs.rs"

[GuillaumeGomez]

The naming of this sub-menu is kinda unclear and definitely doesn't help finding information about docs.rs. So instead, let's rename it "docs.rs" directly to make it more obvious what it actually contains.

[syphar]

Both @Nemo157 and me feel like splitting the menu is better.

• the first two items are about docs.rs (About, privacy)
• the rest are other rust things, could still be named "Rust" or something better?

[syphar]

Awesome, I like it much more!

The gui-tests need fixing, but then I'll approve & merge