Add information to retrieve complete file history

A commit changed the location of source files. Unfortunately, github interface doesn't show the history past this change. Added a documentation based in a stackoverflow post about how to access this history.

Author: franciscojunior

README.md

@@ -36,7 +36,17 @@ Developers who contributes to Npgsql currently or in past, in no particular orde
 
 Refer LICENSE.txt for more information on license terms.
 
+###Code history
+
+On December 2nd, [we committed a change][5] to restructure Npgsql code. This change modified file locations and unfortunately made the complete modification history of those files to not be available anymore through GitHub interface directly. [This stackoverflow post][6] documents a way to access the history before the rename: You just need to access the object tree **before** the rename and then you can see the rest of the file history.
+In the case of this rename, this is the tree: https://github.com/npgsql/Npgsql/tree/2f8928e4dee59275767de0df2ec41a654744a3bc
+
+This will help future searches for the history of the files. Note that you stil can access the complete history of the file through command line: `git log --follow ./newflodername/file`
+
+
 [1]: http://www.npgsql.org/  "Official site"
 [2]: https://github.com/npgsql/Npgsql/  "Npgsql source code @ GitHub"
 [3]: http://www.nuget.org/packages/Npgsql/ "Npgsql @ Nuget Gallery"
 [4]: https://github.com/npgsql/Npgsql/wiki/  "Wiki"
+[5]: https://github.com/npgsql/Npgsql/commit/d7beea23f3407b38747cde05568a59ac87cdd121#diff-3b02da674650ba0f31603c365249f34f
+[6]: http://stackoverflow.com/questions/17213046/see-history-in-github-after-folder-rename