SDK updating, keeping existing git repo intact (wiki update)

[Philip Oakley]

Hi all.

I've added a section to the wiki detailing how I needed to update my SDK
installation because of a pacman gpg lockout that I couldn't get past.
It was the same key that Dscho had noted a few weeks back.

I added the section : If All Else Fails.

https://github.com/git-for-windows/git/wiki/Updating-your-SDK#if-all-else-fails

If anyone has comments, I'm happy to amend (or it is a wiki so..)

Also I have created a pair of ReadMe's for the 32 and 64 bit SDKs so
that they should end up in the contributor's top level directory to give
them pointers as to where the SDK comes from should they have forgotten
about the wiki page..  They are added as PRs so could be rejected /
edited / improved etc.

--

Philip