mako: Add flavours templating start and end strings

Added strings which signify to flavours that it should insert
its theme color template in-between. Since the file is not
symlinked but *moved* to the config dir (through being
designated as 'template' in dotter), any future changes
should not reflect back into the repository.

desktop/.config/mako/config

@@ -9,7 +9,11 @@ default-timeout=5000
 ignore-timeout=1
 font=monospace 14
 
+# Intentionally left empty, automatically filled by flavours
+# on switching theme.
+# Start flavours
 
+# End flavours
 
 [urgency=critical]
 #on-notify=exec mpv /usr/share/sounds/freedesktop/stereo/message.oga