keyword: improve help for kwfiles

- just use "files" instead of "filenames" (analogous to "hg status -h")
- reference the extension help wrt pattern configuration

Kudos to timeless for helpful suggestions.

hgext/keyword.py

@@ -359,16 +359,19 b' def expand(ui, repo, *pats, **opts):'
     _kwfwrite(ui, repo, True, *pats, **opts)
 
 def files(ui, repo, *pats, **opts):
-    '''print filenames configured for keyword expansion
+    '''show files configured for keyword expansion
 
-    Check which filenames in the working directory are matched by the
+    List which files in the working directory are matched by the
     [keyword] configuration patterns.
 
     Useful to prevent inadvertent keyword expansion and to speed up
-    execution by including only filenames that are actual candidates
+    execution by including only files that are actual candidates
     for expansion.
 
-    Use -u/--untracked to display untracked filenames as well.
+    See "hg help keyword" on how to construct patterns both for
+    inclusion and exclusion of files.
+
+    Use -u/--untracked to list untracked files as well.
 
     With -a/--all and -v/--verbose the codes used to show the status
     of files are:

tests/test-keyword.out

@@ -50,7 +50,7 b' list of commands:'
 
  kwdemo     print [keywordmaps] configuration and an expansion example
  kwexpand   expand keywords in the working directory
- kwfiles    print filenames configured for keyword expansion
+ kwfiles    show files configured for keyword expansion
  kwshrink   revert expanded keywords in the working directory
 
 enabled extensions: