docs - add supported GPDB versions to gpbackup/restore requirements
<topic id="topic_vh5_1hd_tbb">
<title>Requirements and Limitations</title>
<body>
- <p>The <codeph>gpbackup</codeph> and <codeph>gprestore</codeph> utilities are available with
- Greenplum Database 5.5.0 and later. </p>
+ <p>The <codeph>gpbackup</codeph> and <codeph>gprestore</codeph> utilities are compatible with
+ these Greenplum Database versions:</p>
+ <ul id="ul_jlm_wnd_hjb">
+ <li>Pivotal Greenplum Database 4.3.22 and later</li>
+ <li>Pivotal Greenplum Database 5.5.0 and later</li>
+ <li>Pivotal Greenplum Database 6.0.0 and later</li>
+ </ul>
<p><codeph>gpbackup</codeph> and <codeph>gprestore</codeph> have the following limitations:<ul
id="ul_uqh_hhd_tbb">
<li>If you create an index on a parent partitioned table, <codeph>gpbackup</codeph> does
