patch 8.1.0495: :filter only supports some commands

Problem:    :filter only supports some commands.
Solution:   Add :filter support for more commands. (Marcin Szamotulski,
            closes #2856)
diff --git a/runtime/doc/various.txt b/runtime/doc/various.txt
index fce8ba1..af49c3e 100644
--- a/runtime/doc/various.txt
+++ b/runtime/doc/various.txt
@@ -565,7 +565,18 @@
 			The pattern is matched against the relevant part of
 			the output, not necessarily the whole line. Only some
 			commands support filtering, try it out to check if it
-			works.
+			works. Some of the commands that support filtering:
+                          |:#|          - filter whole line
+                          |:command|    - filter by command name
+                          |:files|      - filter by file name
+                          |:highlight|  - filter by highlight group
+                          |:jumps|      - filter by file name
+                          |:let|        - filter by variable name
+                          |:list|       - filter whole line
+                          |:llist|      - filter by file name or module name
+                          |:oldfiles|   - filter by file name
+                          |:clist|      - filter by file name or module name
+                          |:set|        - filter by variable name
 
 			Only normal messages are filtered, error messages are
 			not.