Update README.md with repository locations

README.md

@@ -1,6 +1,23 @@
 # DAMASK - The Düsseldorf Advanced Material Simulation Kit
 
-Visit [damask.mpie.de](https://damask.mpie.de) for installation and usage instructions
+- Usage, installation, and support: https://damask.mpie.de
+- Code development: https://git.damask.mpie.de
+- General inquiries: damask@mpie.de
+
+
+## Repository Locations
+
+### [git.damask.mpie.de](https://git.damask.mpie.de)
+
+All code development is centralized in the principal DAMASK code repository hosted at [git.damask.mpie.de](https://git.damask.mpie.de).
+Access to this GitLab instance requires registration and is granted to anyone with an interest in actively supporting the development of DAMASK.
+
+### [github.com](https://github.com)
+
+GitHub hosts the publicly accessible, but read-only, mirror of the principal DAMASK code repository and replicates its three top-level branches from [git.damask.mpie.de](https://git.damask.mpie.de).
+
+The site is primarily meant to provide a forum for [Discussions](https://github.com/eisenforschung/DAMASK/discussions) and [Issues](https://github.com/eisenforschung/DAMASK/issues).
+
 
 ## Contact Information
 
@@ -8,8 +25,3 @@ Max-Planck-Institut für Eisenforschung GmbH
 Max-Planck-Str. 1  
 40237 Düsseldorf  
 Germany  
-
-damask@mpie.de  
-https://damask.mpie.de  
-https://git.damask.mpie.de  
-