Docs - Add RHEL 8 notice for client tools
<ul id="ul_ft3_5jm_3bb">
<li id="pm445741" class="- topic/li ">Red Hat Enterprise Linux x86_64 6.x (RHEL 6)</li>
<li id="pm445741a" class="- topic/li ">Red Hat Enterprise Linux x86_64 7.x (RHEL 7)</li>
+ <li class="- topic/li ">Red Hat Enterprise Linux x86_64 8.x (RHEL 8)</li>
<li>Ubuntu 18.04 LTS</li>
<!-- li dir="ltr">AIX 7.2 (64-bit) (Client and Load Tools only)</li>
<li id="pm445742" class="- topic/li ">SuSE Linux Enterprise Server x86_64 SLES 11</li> -->
