C-LINK should encourage use of intra-rustdoc links over manual linking

[ilyvion]

Since rust-lang/rust#43466 (intra-rustdoc links) was stabilized in Rust 1.48, the information in C-LINK feels outdated, as it still suggests linking to other items manually rather than by making use of intra-rustdoc links:

api-guidelines/src/documentation.md

Lines 147 to 172 in 0e41903

	## Prose contains hyperlinks to relevant things (C-LINK)
	Regular links can be added inline with the usual markdown syntax of
	`[text](url)`. Links to other types can be added by marking them with
	``[`text`]``, then adding the link target in a new line at the end of
	the docstring with ``[`text`]: <target>``, where `<target>` is
	described below.
	Link targets to methods within the same type usually look like this:
	```md
	[`serialize_struct`]: #method.serialize_struct
	```
	Link targets to other types usually look like this:
	```md
	[`Deserialize`]: trait.Deserialize.html
	```
	Link targets may also point to a parent or child module:
	```md
	[`Value`]: ../enum.Value.html
	[`DeserializeOwned`]: de/trait.DeserializeOwned.html
	```