Change "learn more" to "more details about this file"

Several people complained that "Learn more on Wikimedia Commons"
is not clear: it can be interpreted as a link to the Commons
main page, the text does not suggest that the link will be related
to this specific file. The new wording tries to address this.

Change-Id: Ia605cc30c4ca57598f7cebdde60061800a10b6e7
Merge "Change "learn more" to "more details about this file""