Thanks to the following (awesome) blog post: http://blog.ryankempt.com/2012/09/windows-library-add-non-indexed-location.html, today I was able to add/show non-indexed network locations into my Documents Library.

This workaround is especially useful whenever you're storing, say, your family Pictures on a (Linux-based) NAS that does not support indexing.

For convenience’s sake, I’ll report what's involved the way "it worked for me":

1. Win+E –> C:\Users\%username%\AppData\Roaming\Microsoft\Windows\Libraries\
2. Right-Click on the Library you wish to customise (ie. Pictures).
3. Select "Open with..." and open w/your fav txt editor.
4. Scroll to EOF and locate the last "</searchConnectorDescription>".
5. Copy the following code:

   <searchConnectorDescription>
   <isDefaultSaveLocation>false</isDefaultSaveLocation>
   <isDefaultNonOwnerSaveLocation>false</isDefaultNonOwnerSaveLocation>
   <isSupported>true</isSupported>
   <simpleLocation>
   <url>\\your-file-share\location\folder</url>
   </simpleLocation>
   </searchConnectorDescription>
   </searchConnectorDescriptionList>

6. Paste the above code BEFORE "</searchConnectorDescriptionList>" AND BELOW/AFTER the last "</searchConnectorDescription>".
7. Update "<url>\\your-file-share\location\folder</url>" with your desired Network Location.
8. Save and close, then browse to, say, your Pictures Library (as you normally would).

[BONUS UPDATE]: On Windows 8/8.1, Libraries have been disabled (by default).

To enable/show Libraries on your folders list, proceed as follows:

SRC: http://blog.ryankempt.com/2012/09/windows-library-add-non-indexed-location.html