Add prologue text for list of potential checkers.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@165705 91177308-0d34-0410-b5e6-96231b3b80d8

www/analyzer/potential_checkers.html

@@ -18,6 +18,8 @@
 <div id="content">
 <h1>List of potential checkers</h1>
 
+<p>This page contains a list of potential checkers to implement in the static analyzer.  If you are interested in contributing to the analyzer's development, this is a good resource to help you get started.  The specific names of the checkers are subject to review, and are provided here as suggestions.</p>
+
 <!-- ========================= allocation/deallocation ======================= -->
 <h3>allocation/deallocation</h3>
 <table class="checkers">