Add link to VisIt 3.1.2 Ubuntu20 release on executables page.
Ubuntu 19, 4.9.184-linuxkit #1 SMP, gcc 8.3</td>
<td><a href="https://github.com/visit-dav/visit/releases/download/v3.1.2/visit3_1_2.linux-x86_64-ubuntu19.tar.gz">Download</a></td>
</tr>
+ <tr>
+ <td>Linux - x86_64 64 bit<br />
+ Ubuntu 20, 4.19.76-linuxkit #1 SMP, gcc 9.3</td>
+ <td><a href="https://github.com/visit-dav/visit/releases/download/v3.1.2/visit3_1_2.linux-x86_64-ubuntu20.tar.gz">Download</a></td>
+ </tr>
<tr>
<td>Linux - x86_64 64 bit<br />
Debian 9, 4.9.184-linuxkit #1 SMP, gcc 6.3<br />
