Point out where general/specific attribute docs split

Author: Havvy

src/attributes.md

@@ -28,7 +28,7 @@ and language and compiler version. Attributes are modeled on Attributes in
 
 Attributes may appear as any of:
 
-* A single identifier, the attribute name
+* A single identifier, the _attribute name_
 * An identifier followed by the equals sign '=' and a literal, providing a
   key/value pair
 * An identifier followed by a parenthesized literal, providing a
@@ -72,6 +72,9 @@ mod bar {
 type int8_t = i8;
 ```
 
+The rest of this page describes or links to descriptions of which attribute
+names have meaning.
+
 ## Crate-only attributes
 
 - `crate_name` - specify the crate's crate name.