doc/install.html: update wrt to OS and compiler support. Update issue 7188 Fixes issue 7894.
doc/install.html: update wrt to OS and compiler support.
Update issue 7188
Fixes issue 7894.

LGTM=alex.brainman, bradfitz, r
R=golang-codereviews, alex.brainman, mikioh.mikioh, gobot, r, bradfitz
CC=golang-codereviews
https://codereview.appspot.com/95870043

wesolows/golang,wesolows/golang,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang,firebitsbr/golang-old,wesolows/golang,wesolows/golang,wesolows/golang,wesolows/golang,firebitsbr/golang-old,wesolows/golang-old,firebitsbr/golang-old