Create git-sd.md

Add some information for sd users about starting with git. [skip ci]

docs/git-sd.md

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+# Quick git-primer for sd users
+
+There few important conceptual differences with **sd**.
+This list tries to bridge the gap
+
+* When you do `git commit` changes are stored in your local clone of the repo. 
+To Submit them, you need to do `git push`.
+* Forks are just a way to store branches. 
+You can push branch to the original repo (if you have permissions) or to the fork. 
+There is no principal difference.
+* Most of the git complications come from the fact that you need to do integrations by yourself.
+
+### Rosetta stone
+
+
+#### Concepts
+
+| Concept | SD termin | Git termin |
+|---------|----|----------------|
+| Your local copy | enlistment | cloned repo |
+| Code changes  | changelist | commit |
+| Way to preserve changes locally | dpk | local branch |
+
+
+#### Commands 
+
+Before running a git command for the first time, try
+
+```sh
+git help <command name>
+```
+
+To read about flags and the overall meaning.
+
+|Scenarios | SD command | Git commmand |
+|---------|----|----------------|
+| Get the code at the first place | sd enlist | git clone |
+| Sync changes  |  sd sync | git pull |
+| Add new files |  sd add  | git add |
+| Modify existing files | sd edit | git add |
+| Remove existing files | sd delete | git rm |
+| Copy/Rename files | sd branch | git mv |
+| Commit to local |   | git commit |
+| Submit changes | sd submit | git push |
+| Revert changes | sd revert | git checkout |
+| Undo submitted changes | sd undo | git revert |
+| Diff tool | odd | git diff |
+| Clean enlistment  |  build nuke | git clean |
+