doc: remove note about installing from source for ARM

Now there are ARM downloads too.

Change-Id: I236381508c69d56748e672d184b92caa715e81ae
Reviewed-on: https://go-review.googlesource.com/18342
Reviewed-by: Andrew Gerrand <adg@golang.org>

doc/install.html

@@ -48,7 +48,7 @@ <h2 id="requirements">System requirements</h2>
 </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; install from source for ARM</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>Mac OS X 10.7 or later</td> <td>amd64</td> <td>use the clang or gcc<sup>&#8224;</sup> that comes with Xcode<sup>&#8225;</sup></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>