Expand LangRef.html's documentation on LLVM's inline assembly.

While trying to figure out how this was all supposed to work, I
figured I'd start writing down some documentation, since it was
basically completely missing.

Differential Revision: http://reviews.llvm.org/D10816

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@241698 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed