doc: mention more binary download architectures

Fixes #18207

Change-Id: Ibe85ab0acba7553b93603a31140b31bd9e4802cf
Reviewed-on: https://go-review.googlesource.com/34015
Reviewed-by: Ian Lance Taylor <[email protected]>

Author: bradfitz

doc/install.html

@@ -47,8 +47,8 @@ <h2 id="requirements">System requirements</h2>
 <th align="center">Notes</th>
 </tr>
 <tr><td colspan="3"><hr></td></tr>
-<tr><td>FreeBSD 8-STABLE or later</td> <td>amd64</td> <td>Debian GNU/kFreeBSD not supported</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</td></tr>
+<tr><td>FreeBSD 8-STABLE or later</td> <td>amd64, 386</td> <td>Debian GNU/kFreeBSD not supported</td></tr>
+<tr><td>Linux 2.6.23 or later with glibc</td> <td>amd64, 386, arm, s390x, ppc64le</td> <td>CentOS/RHEL 5.x not supported</td></tr>
 <tr><td>Mac OS X 10.8 or later</td> <td>amd64</td> <td>use the clang or gcc<sup>&#8224;</sup> that comes with Xcode<sup>&#8225;</sup> for <code>cgo</code> support</td></tr>
 <tr><td>Windows XP or later</td> <td>amd64, 386</td> <td>use MinGW gcc<sup>&#8224;</sup>. No need for cygwin or msys.</td></tr>
 </table>