updated git instructions

Author: oscarjalnefjord

doc/setting_up_git.md

@@ -1,2 +1,8 @@
 ## Installing Git
-To install a fresh copy of Git or to upgrade to the latest version, please follow the instructions outlined in: [Installing Git](https://git-scm.com/book/en/v2/Getting-Started-Installing-Git)
+To install a fresh copy of Git or to upgrade to the latest version, please follow the instructions outlined in: [Installing Git](https://git-scm.com/book/en/v2/Getting-Started-Installing-Git)
+
+Before you start using Git you need set your username and e-mail with the commands:
+```
+git config --global user.name "FIRST_NAME LAST_NAME"
+git config --global user.email "MY_NAME@example.com"
+```