update CONTRIBUTING.md (#191)

Author: bernhardmgruber

CONTRIBUTING.md

@@ -9,7 +9,12 @@ Suport for clang-format is built-in since Visual Studio 2017 15.7 and CLion 2019
 The .clang-format file in the repository will be automatically detected and formatting is done as you type, or triggered when pressing the format hotkey.
 
 ### Bash
-First install clang-format. Instructions therefore can be found on the web. To format you can run this command in bash:
+First install clang-format. Instructions therefore can be found on the web.
+To format your changes since branching off `dev`, you can run this command in bash:
 ```
-find -iname *.cu -o -iname *.hpp | xargs clang-format-10 -i
+git clang-format dev
+```
+To format all code in your working copy, you can run this command in bash:
+```
+find -iname *.cpp -o -iname *.hpp | xargs clang-format -i
 ```