Add git-active utility

@@ -193,10 +193,13 @@
           sort > ~/unref-i386.out
         $ findunref $SPARCSRC $SPARCSRC/tools/findunref/exception_list | \
           sort > ~/unref-sparc.out
         $ comm -12 ~/unref-i386.out ~/unref-sparc.out > ~/unref.out
 
+git-active
+        helper used by webrev to generate file lists for Git workspaces.
+
 hdrchk
         checks headers for compliance with OS/Net standards (form, includes,
         C++ guards).
 
 hgsetup