[readme] Add local modifications section

Change-Id: I5966bcbfed467b140b89e9162af3df7555472a35
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/markupsafe/+/494882
Reviewed-by: Shai Barack <shayba@google.com>
diff --git a/README.fuchsia b/README.fuchsia
index 7662bee..ece1bb7 100644
--- a/README.fuchsia
+++ b/README.fuchsia
@@ -9,3 +9,6 @@
 string escaping. It is used by Jinja 2, the Mako templating engine, the
 Pylons web framework and many more.
 
+Local Modifications:
+Added README.fuchsia.
+Added py_srcs.gni.