Added about git-submodule usage

README

@@ -14,9 +14,9 @@ files include useful constants which will be available with "include <MCAD/*.sca
 which should be safe to use on all included files (ie. no top level code should
 create geometry).
 
-If you host your project in git, you use "git submodule add URL" in your
-repo to import this library as a git submodule for easy usage. See
-"git help submodule"" for more info
+If you host your project in git, you can do "git submodule add URL" in your
+repo to import this library as a git submodule for easy usage. Then you need to do a "git submodule update --init MODULE". See
+"git help submodule"" for more info.
 
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