Rollup merge of rust-lang#62595 - ngoldbaum:path-clarity-doc, r=Centril

Document that the crate keyword refers to the project root

:wave: this is my first rust contribution so I hope I'm doing everything correctly. Help very much appreciated if I'm not.

As far as I can tell this use of `crate` is only documented [in the edition guide for rust 2018](https://doc.rust-lang.org/edition-guide/rust-2018/module-system/path-clarity.html#the-crate-keyword-refers-to-the-current-crate). However it should probably be in the documentation for the `crate` keyword itself. This adds that documentation.

Author: Centril

src/libstd/keyword_docs.rs

@@ -119,7 +119,7 @@ mod continue_keyword { }
 /// The `as` keyword can be used to change what the crate is referred to as in your project. If a
 /// crate name includes a dash, it is implicitly imported with the dashes replaced by underscores.
 ///
-/// `crate` is also used as in conjunction with `pub` to signify that the item it's attached to
+/// `crate` can also be used as in conjunction with `pub` to signify that the item it's attached to
 /// is public only to other members of the same crate it's in.
 ///
 /// ```rust
@@ -131,6 +131,10 @@ mod continue_keyword { }
 /// }
 /// ```
 ///
+/// `crate` is also used to represent the absolute path of a module, where `crate` refers to the
+/// root of the current crate. For instance, `crate::foo::bar` refers to the name `bar` inside the
+/// module `foo`, from anywhere else in the same crate.
+///
 /// [Reference]: ../reference/items/extern-crates.html
 mod crate_keyword { }