Merge pull request #321 from sbriseid/install_info

Emphasized importance of sub-module initializing.

Author: sbriseid

INSTALL

@@ -7,7 +7,8 @@ Git
 The gotools module points to a repository on GitHub:
 https://github.com/SINTEF-Geometry/GoTools.git.
 
-GoTools contains two submodules (on GitHub):
+GoTools contains three submodules (on GitHub):
+GoTools-Data: https://github.com/SINTEF-Geometry/GoTools-Data.git,
 SISL: https://github.com/SINTEF-Geometry/SISL.git, and
 TTL: https://github.com/SINTEF-Geometry/TTL.git.
 
@@ -19,6 +20,10 @@ Alternatively use ssh:
 
 $ git clone --recursive [email protected]:SINTEF-Geometry/GoTools.git
 
+Initialize the submodules (not necessary if the clone-step used "--recursive"):
+
+$ git submodule update --init
+
 The branch 'master' is the only branch. Any releases will be available as tags.
 
 CMake