Target maintainers: doc/install.texi love and care

[Palmer Dabbelt]

On Sun, 12 Mar 2017 04:27:26 PDT (-0700), gerald@pfeifer.com wrote:
> I noticed that the target-specific sections in doc/install.texi
> need a little lover and care.  It would be great could you have
> a look and streamline/update before the GCC 7 release.

I looked at our stuff (RISC-V) and there's almost nothing in there.  Is there
something I should add?  I looked at the aarch64 stuff in the "host/target
specific issues start here" section and there's some notes about binutils-2.24.
We'll require binutils-2.28 (the first version that we're upstream in), I can
add a note in that section about RISC-V as well if you think it's appropriate.