document submodule usage

Signed-off-by: Alon Levy <alon@pobox.com>

diff --git a/extlib/README b/extlib/README
index a2cc6ec02885b03bbc0b96bc4783b01d963da4b9..45ee5b46125cbb11faff888b79a8e9006c8d8ed3 100644 (file)
--- a/extlib/README
+++ b/extlib/README
@@ -63,6 +63,19 @@ FAQ
     This is a last resort; consult with the rest of the dev group
     before taking this radical step.
 
+:Q: What about submodules?
+
+:A: pdf.js is supplied as a submodule, and other software may use that too,
+    to add a new submodule:
+     git submodule add <git-repo-of-fun-project> extlib/fun-project
+
+    Use it just like a snapshotted extlib directory. When a new clone of mediagoblin
+    is made you need to run
+
+     git submodule init
+     git submodule update
+
+    As noted in HackingHowto
 
 Thanks
 ======