.mailmap/aliases: add some further commentary

The two files are not interchangeable but a change to one *might*
require a change to the other so lets flag that up with an explanation
of what both files are trying to achieve. While we are at it document
the many forms .mailmap can take in the header.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Aleksandar Markovic <amarkovic@wavecomp.com>

.mailmap

@@ -1,4 +1,18 @@
 # This mailmap fixes up author names/addresses.
+#
+# If you are adding to this file consider if a similar change needs to
+# be made to contrib/gitdm/aliases. They are not however completely
+# analogous. .mailmap is concerned with fixing up damaged author
+# fields where as the gitdm equivalent is more concerned with making
+# sure multiple email addresses get mapped onto the same author.
+#
+# From man git-shortlog the forms are:
+#
+#  Proper Name <commit@email.xx>
+#  <proper@email.xx> <commit@email.xx>
+#  Proper Name <proper@email.xx> <commit@email.xx>
+#  Proper Name <proper@email.xx> Commit Name <commit@email.xx>
+#
 
 # The first section translates weird addresses from the original git import
 # into proper addresses so that they are counted properly by git shortlog.

contrib/gitdm/aliases

@@ -1,6 +1,22 @@
 #
-# This is the email aliases file, mapping secondary addresses
+# This is the email aliases file, mapping secondary addresses onto a
-# onto a single, canonical address. Duplicates some info from .mailmap
+# single, canonical address. It duplicates some info from .mailmap so
+# if you are adding something here also consider if the .mailmap needs
+# updating.
+#
+# If you just want to avoid gitdm complaining about author fields
+# which are actually email addresses with the message:
+#
+#   "...is an author name, probably not what you want"
+#
+# you can just apply --use-mailmap to you git-log command, e.g:
+#
+#   git log --use-mailmap --numstat --since "last 2 years" | $GITDM
+#
+# however that will have the effect of squashing multiple addresses to
+# a canonical address which will distort the stats of those who
+# contribute in both personal and professional capacities from
+# different addresses.
 #
 
 # weird commits

contrib/gitdm/group-map-individuals

@@ -2,7 +2,8 @@
 # Individual and personal contributors
 #
 # This is simply to allow prolific developers with no company
-# affiliations to be grouped together in the summary stats.
+# affiliations (or non-company related personal work) to be grouped
+# together in the summary stats.
 #
 
 f4bug@amsat.org