README: provide some more explanation about TLS
diff --git a/README.md b/README.md
index b9a42d7..8829242 100644
--- a/README.md
+++ b/README.md
@@ -70,7 +70,10 @@ before calling any other libgit2 functions. You can call this function many time
git_libgit2_shutdown();
-will free the resources.
+will free the resources. Note that if you have worker threads, you should
+call `git_libgit2_shutdown` *after* those threads have exited. If you
+require assistance coordinating this, simply have the worker threads call
+`git_libgit2_init` at startup and `git_libgit2_shutdown` at shutdown.
Threading
=========