add Git index

doc/topics/git/index.md

+# Git documentation
+
+## Getting started
+
+- [Git concepts](../university/training/user_training.html#git-concepts)
+- [Start using Git on the command line](../gitlab-basics/start-using-git.html)
+- [Command Line basic commands](../gitlab-basics/command-line-commands.html)
+- [GitLab Git Cheat Sheet (download)](https://gitlab.com/gitlab-com/marketing/raw/master/design/print/git-cheatsheet/print-pdf/git-cheatsheet.pdf)
+- **Articles:**
+  - [Git Tips & Tricks](https://about.gitlab.com/2016/12/08/git-tips-and-tricks/)
+- **Third-party resources:**
+  - What is [Git](https://git-scm.com)
+    - [Version control](https://git-scm.com/book/en/v2/Getting-Started-About-Version-Control)
+    - [Getting Started - Git Basics](https://git-scm.com/book/en/v2/Getting-Started-Git-Basics)
+    - [Getting Started - Installing Git](https://git-scm.com/book/en/v2/Getting-Started-Installing-Git)
+    - [Git on the Server - GitLab](https://git-scm.com/book/en/v2/Git-on-the-Server-GitLab)
+
+### Branching strategies
+
+- **Articles:**
+  - [GitLab Flow](https://about.gitlab.com/2014/09/29/gitlab-flow/)
+- **Third-party resources:**
+  - [Git Branching - Branches in a Nutshell](https://git-scm.com/book/en/v2/Git-Branching-Branches-in-a-Nutshell)
+  - [Git Branching - Branching Workflows](https://git-scm.com/book/en/v2/Git-Branching-Branching-Workflows)
+
+### Version control
+
+- **Presentations:**
+  - [GLU Course: About Version Control](https://docs.google.com/presentation/d/16sX7hUrCZyOFbpvnrAFrg6tVO5_yT98IgdAqOmXwBho/edit?usp=sharing)
+
+## Advanced use
+
+- [Custom Git Hooks](../administration/custom_hooks.html)
+- [Git Attributes](../user/project/git_attributes.html)
+- Git Submodules: [Using Git submodules with GitLab CI](../ci/git_submodules.html#using-git-submodules-with-gitlab-ci)
+
+## API
+
+- [Gitignore templates](../api/templates/gitignores.html)
+
+## Git LFS
+
+- [Git LFS](https://docs.gitlab.com/ce/workflow/lfs/manage_large_binaries_with_git_lfs.html)
+- **Articles:**
+  - [Getting Started with Git LFS](https://about.gitlab.com/2017/01/30/getting-started-with-git-lfs-tutorial/)
+  - [Git-Annex to Git-LFS migration guide](https://docs.gitlab.com/ee/workflow/lfs/migrate_from_git_annex_to_git_lfs.html)