Improve docs for URLEqualsHashCode.

PiperOrigin-RevId: 652878662

Author: cpovirk

docs/bugpattern/URLEqualsHashCode.md

@@ -1,2 +1,7 @@
-Equals and HashCode method of java.net.URL make blocking network calls. Either
-use java.net.URI or if that isn't possible, use Collection<URL> or List<URL>.
+The `equals` and `hashCode` methods of `java.net.URL` make blocking network
+calls. When you place a `URL` into a hash-based container, the container invokes
+those methods.
+
+Prefer `java.net.URI`. Or, if you must use `URL` in a
+collection, prefer to use a non-hash-based container like a `List<URL>`, and
+avoid calling methods like `contains` (which calls `equals`) on it.