Add new location where templates and locales are found.

Needed to document the 'pip install' location of the templates/locales
and other shared files (e.g. man pages).

Author: rouilj

doc/tracker_templates.txt

@@ -11,13 +11,20 @@ The template loading looks in four places to find the templates:
 
 1. *share* - eg. ``<prefix>/share/roundup/templates/*``.
    This should be the standard place to find them when Roundup is
-   installed.
-2. ``<roundup.admin.__file__>/../templates/*``.
+   installed running setup.py from source.
+2. ``install_dir``/../<prefix>/share/....``, where prefix is the
+   Python's ``sys.prefix``. This finds templates (and locales)
+   installed by pip. E.G. in a virtualenv located at (``sys.prefix``):
+   ``/tools/roundup``, roundup would be at:
+   ``/tools/roundup/lib/python3.6/site-packages/roundup``. The
+   templates would be at:
+   ``/tools/roundup/lib/python3.6/site-packages/tools/roundup/share/roundup/templates/``.
+3. ``<roundup.admin.__file__>/../templates/*``.
    This will be used if Roundup's run in the distro (aka. source)
    directory.
-3. ``<current working dir>/*``.
+4. ``<current working dir>/*``.
    This is for when someone unpacks a 3rd-party template.
-4. ``<current working dir>``.
+5. ``<current working dir>``.
    This is for someone who "cd"s to the 3rd-party template dir.
 
 Templates contain: