Add find module `patterns` option use cases documentation (#57089)

* Specify that the pattern is matched against the dirent basename
* Specify that regexen must match the whole name of the dirent. It has been a pitfall for me.

lib/ansible/modules/files/find.py

@@ -37,6 +37,10 @@ options:
             - One or more (shell or regex) patterns, which type is controlled by C(use_regex) option.
             - The patterns restrict the list of files to be returned to those whose basenames match at
               least one of the patterns specified. Multiple patterns can be specified using a list.
+            - The pattern is matched against the file base name, excluding the directory.
+            - When using regexen, the pattern MUST match the ENTIRE file name, not just parts of it. So
+              if you are looking to match all files ending in .default, you'd need to use '.*\.default'
+              as a regexp and not just '\.default'.
             - This parameter expects a list, which can be either comma separated or YAML. If any of the
               patterns contain a comma, make sure to put them in a list to avoid splitting the patterns
               in undesirable ways.