Clarified all attributes which prompt warnings

All calls which trigger rustdoc warnings and are now properly verbose for consistency. This uses the attribute in the examples which provides the user with more context.

Author: simbleau

src/doc/rustdoc/src/lints.md

@@ -70,6 +70,8 @@ This lint **warns by default**. This lint detects when [intra-doc links] from pu
 For example:
 
 ```rust
+#![warn(private_intra_doc_links)]
+
 /// [private]
 pub fn public() {}
 fn private() {}
@@ -302,6 +304,8 @@ This lint is **warn-by-default**. It detects URLs which are not links.
 For example:
 
 ```rust
+#![warn(bare_urls)]
+
 /// http://example.org
 /// [http://example.net]
 pub fn foo() {}