docs: process/5.Posting.rst: clarify use of Reported-by: tag

Bring the description on when to use the Reported-by: tag found in
Documentation/process/5.Posting.rst more in line with the description in
Documentation/process/submitting-patches.rst: before this change the two
were contradicting each other, as the latter is way more permissive and
only states '[...] if the bug was reported in private, then ask for
permission first before using the Reported-by tag.'
Signed-off-by: Thorsten Leemhuis <linux@leemhuis.info>
Link: https://lore.kernel.org/r/2fc7162dfb76e04da5ea903c9c170d913e735dad.1664372256.git.linux@leemhuis.infoSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/process/5.Posting.rst

@@ -256,8 +256,10 @@ The tags in common use are:
  - Cc: the named person received a copy of the patch and had the
    opportunity to comment on it.
 
-Be careful in the addition of tags to your patches: only Cc: is appropriate
-for addition without the explicit permission of the person named.
+Be careful in the addition of tags to your patches, as only Cc: is appropriate
+for addition without the explicit permission of the person named; using
+Reported-by: is fine most of the time as well, but ask for permission if
+the bug was reported in private.
 
 
 Sending the patch