Add note about what to do with submodules on first checkout.

Technotes/SubmoduleCheatSheet.md

@@ -2,6 +2,12 @@
 
 Evergreen uses [Git submodules](https://git-scm.com/book/en/v2/Git-Tools-Submodules) to include shared frameworks. At this writing (June 2018) they are DB5, RSCore, RSDatabase, RSWeb, RSTree, and RSParser.
 
+After your first checkout:
+
+	git submodule init
+  git submodule update
+
+
 To add a submodule:
 
 	git submodule add https://github.com/username/path