doc/install.html: update wrt to OS and compiler support.

Update #7188
Fixes #7894.

LGTM=alex.brainman, bradfitz, r
R=golang-codereviews, alex.brainman, mikioh.mikioh, gobot, r, bradfitz
CC=golang-codereviews
https://golang.org/cl/95870043

doc/install.html

@@ -44,10 +44,10 @@ proceeding. If your OS or architecture is not on the list, it's possible that
 <th align="middle">Notes</th>
 </tr>
 <tr><td colspan="3"><hr></td></tr>
-<tr><td>FreeBSD 7 or later</td> <td>amd64, 386, arm</td> <td>Debian GNU/kFreeBSD not supported; FreeBSD/ARM needs FreeBSD 10 or later</td></tr>
+<tr><td>FreeBSD 8 or later</td> <td>amd64, 386, arm</td> <td>Debian GNU/kFreeBSD not supported; FreeBSD/ARM needs FreeBSD 10 or later</td></tr>
 <tr><td>Linux 2.6.23 or later with glibc</td> <td>amd64, 386, arm</td> <td>CentOS/RHEL 5.x not supported; no binary distribution for ARM yet</td></tr>
 <tr><td>Mac OS X 10.6 or later</td> <td>amd64, 386</td> <td>use the gcc<sup>&#8224;</sup> that comes with Xcode<sup>&#8225;</sup></td></tr>
-<tr><td>Windows 2000 or later</td> <td>amd64, 386</td> <td>use mingw gcc<sup>&#8224;</sup>; cygwin or msys is not needed</td></tr>
+<tr><td>Windows XP or later</td> <td>amd64, 386</td> <td>use MinGW gcc<sup>&#8224;</sup>. No need for cgywin or msys.</td></tr>
 </table>
 
 <p>