Merge pull request #13777 from frankyn/patch-1

[Ruby] Specify module init in README
diff --git a/src/ruby/README.md b/src/ruby/README.md
index 5c7dae6..f6fce3e 100644
--- a/src/ruby/README.md
+++ b/src/ruby/README.md
@@ -22,6 +22,12 @@
 ---------------------
 - Clone this repository
 
+- Init submodules
+
+```sh
+git submodule update --init
+```
+
 - Install Ruby 2.x. Consider doing this with [RVM](http://rvm.io), it's a nice way of controlling
   the exact ruby version that's used.
 ```sh