Bug 13314: Follow-up for m.de.rooy in .mailmap

Email addresses in git seem to be case sensitive.
The list of shortlog -ns was good, but git shortlog -e still made a
difference.
Additionally, reworded initial comments slightly.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>

.mailmap

@@ -1,6 +1,6 @@
 # This file maintains name/email mappings for git-shortlog use
-# For more information on the use of this file see '$ git shortlog -h'
-# Name to mail mapping: the name in the right column will be mapped to the email addy in the left
+# For more information on the use of this file see: man git-shortlog
+# Mail to name mapping: email at the right is mapped to name at the left
 
 James Mason                     <mason@kohaaloha.com>
 Henri-Damien Laurent            <henridamien.laurent@biblibre.com>
@@ -83,3 +83,5 @@ Fridolin Somers                 Fridolyn SOMERS
 <benjamin.rokseth@kul.oslo.kommune.no>    <bensinober@gmail.com>
 <z.tajoli@cineca.it>               <tajoli@cilea.it>
 <z.tajoli@cineca.it>               <ztajoli@gmail.com>
+<m.de.rooy@rijksmuseum.nl>         <M.de.Rooy@rijksmuseum.nl>
+<m.de.rooy@rijksmuseum.nl>         <marcel@libdevelop.rijksmuseum.nl>