- Document new valid-types behavior

Author: brettz9

.README/rules/valid-types.md

@@ -2,6 +2,18 @@
 
 Requires all types to be valid JSDoc or Closure compiler types without syntax errors.
 
+Also impacts behaviors on namepath-pointing or event-pointing tags:
+
+1.  `@alias`, `@augments`, `@extends`, `@lends`, `@memberof`, `@memberof!`, `@mixes`, `@name`, `@this`
+1.  `@callback`, `@event`, `@listens`, `@fires`, `@emits`
+1.  `@borrows`
+
+The following apply to the above sets:
+
+-   Expect tags in set 1 or 2 to have a valid namepath if present
+-   Prevent set 2 from being empty by setting `allowEmptyNamepaths` to `false` as these tags might have some indicative value without a path (but set 1 will always fail if empty)
+-   For the special case of set 3, i.e., `@borrows <that namepath> as <this namepath>`, check that both namepaths are present and valid and ensure there is an `as ` between them.
+
 |||
 |---|---|
 |Context|`ArrowFunctionExpression`, `FunctionDeclaration`, `FunctionExpression`|