Merge branch 'starting_shell' into 'master'

Starting shell document to GitLab basics

I added a new branch for all the changes on this MR https://dev.gitlab.org/gitlab/gitlabhq/merge_requests/1863

Everything should look nicer now :)

See merge request !1869

doc/gitlab_basics/README.md

+# GitLab basics
+
+Step-by-step guides on the basics of working with Git and GitLab.
+
+* [Start using Git on the commandline](start_using_git.md)
+
+

doc/gitlab_basics/start_using_git.md

+# Start using Git on the commandline
+
+If you want to start using a Git and GitLab, make sure that you have created an account on [gitlab.com](https://about.gitlab.com/)
+
+## Open a shell
+
+* Depending on your operating system, find the shell of your preference. Here are some suggestions
+
+- [Terminal](http://blog.teamtreehouse.com/introduction-to-the-mac-os-x-command-line) on  Mac OSX
+
+- [GitBash](https://msysgit.github.io) on Windows
+
+- [Linux Terminal](http://www.howtogeek.com/140679/beginner-geek-how-to-start-using-the-linux-terminal/) on Linux
+
+## Check if Git has already been installed
+
+* Git is usually preinstalled on Mac and Linux
+
+* Type the following command and then press enter
+
+```
+git --version
+```
+
+* You should receive a message that will tell you which Git version you have in your computer. If you don’t receive a "Git version" message, it means that you need to [download Git](https://git-scm.com/book/en/v2/Getting-Started-Installing-Git)
+
+* If Git doesn't automatically download, there's an option on the website to [download manually](https://git-scm.com/downloads). Then follow the steps on the installation window
+
+* After you finished installing, open a new shell and type "git --version" again to verify that it was correctly installed
+
+## Add your Git username and set your email
+
+* It is important because every Git commit that you create will use this information
+
+* On your shell, type the following command to add your username
+
+```
+git config --global user.name ADD YOUR USERNAME
+```
+
+* Then verify that you have the correct username
+
+```	
+git config --global user.name
+```
+
+* To set your email address, type the following command
+
+```
+git config --global user.email ADD YOUR EMAIL
+```
+
+* To verify that you entered your email correctly, type
+
+```		
+git config --global user.email
+```
+
+* You'll need to do this only once because you are using the "--global" option. It tells Git to always use this information for anything you do on that system. If you want to override this with a different username or email address for specific projects, you can run the command without the "--global" option when you’re in that project
+
+## Check your information
+
+* To view the information that you entered, type
+
+```		
+git config --global --list
+```