Add two points to release notes about recent command line library changes.

Patch by Dan Liew!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181335 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/docs/CommandLine.rst b/docs/CommandLine.rst
index 263a025..9b77a98 100644
--- a/docs/CommandLine.rst
+++ b/docs/CommandLine.rst
@@ -618,6 +618,8 @@
     -help             - display available options (-help-hidden for more)
     -o <filename>     - Specify output filename
 
+.. _grouping options into categories:
+
 Grouping options into categories
 --------------------------------