[PATCH] Add user documentation for cpp11-migrate

[Sean Silva]

  > Sean, what do you think about about adding examples of risky transformations after committing this as an initial version?

  That sounds like a good idea. @jy7.yang, could you prepare an updated patch (2, actually: 1 for bare-bones sphinx setup, 1 for adding the man page). I'm currently impartial regarding putting this in clang-tools-extra/docs/ or clang/docs/, so do whatever you want there; it will be easy enough to fix later.

  > There's one more 'auto' transformation in review now, and we do need to put documentation somewhere. We don't have to make it perfect in a single commit.

  That's what spurred me to ping this ;)

http://llvm-reviews.chandlerc.com/D339