Add note on kw expressions' need to be starting the line

src/ffoo/saturnin_www.sh

     # URIs, then equal sign expressions, then things that looked like
     # kw expressions, converted to URIs.
     #
+    # Note that kw expressions (e.g. "bug 123") work only if they start
+    # the line.
+    #
     # Apply this filter to args or clipboard, and either use head -1 or
     # if you are brave, open all URIs.
     #