DOC: First draft to help getting the code

doc_developer/getting_the_code.md

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+# Getting the code
+
+This document explains how to get the source code for NumPy-Financial using Git.
+
+## Code Location
+
+NumPy-Financial is hosted on GitHub. The repository URL is https://github.com/numpy/numpy-financial.
+
+## Creating a fork
+
+To create a fork click the green "fork" button at the top right of the page. This creates a new repository on your
+GitHub profile. This will have the URL: https://github.com/<your_username>/numpy-financial.
+
+## Cloning the repository
+
+Now that you have forked the repository you will need to clone it. This copies the repository from GitHub to the local
+machine. To clone a repository enter the following commands in the terminal.
+
+```shell
+git clone https://github.com/<your_username>/numpy-financial.git
+```
+
+Hooray! You now have a working copy of NumPy-Financial.
+
+
+## Updating the code with other's changes
+
+From time to time you may want to pull down the latest code. Do this with:
+
+```shell
+git fetch
+```
+
+The `git fetch` command downloads commits, files and refs from a remote repo into your local repo.
+
+Then run:
+
+```shell
+git merge --ff-only
+```
+
+The `git merge` command is Git's way of putting independent branches back together. The `--ff-only` flag tells git to
+use `fast-forward` merges. This is preferable as fast-forward merge avoids creating merge commits.