BRANCHES.md: Add explanation of branches and using forks

Author: Kevin Willford

BRANCHES.md

@@ -0,0 +1,51 @@
+Branches used in this repo
+==========================
+
+The document explains the branching structure that we are using in the git for VFSForGit repository as well as the forking strategy that we have adopted for contributing.
+
+Repo Branches
+-------------
+
+1. master
+    
+    This will track the git for windows repository master branch
+
+2. vfs
+    
+    Would like to use this branch as an ever-green branch that continually rebases the VFSForGit changes onto a windows ever-green branch that is on the core/master, so that we can detect when the patches for VFSForGit have issues or if we have a new version patches sent upstream git we can regenerate this branch.
+
+3. vs/master
+    
+    This tracks with the git for windows repository vs/master branch and are the generated files for using a Visual Studio solution.
+
+4. vfs-#
+
+    These branches are used to track the specific version that match git for windows with the VFSForGit specific patches on top.  When a new version of git for windows is released, the VFSForGit patches will be rebased on that windows version and a new gvfs-# branch created to create pull requests against.
+
+    #### Examples
+    ```
+    vfs-2.20.0
+    vfs-2.20.1
+    ```
+
+    The versions of git for VFSForGit are based on the git for windows versions.  v2.20.0.vfs.1 will correspond with the v2.20.0.windows.1 with the VFSForGit specific patches applied to the windows version. 
+
+Tags
+----
+
+We are using annotated tags to build the version number for git.  The build will look back through the commit history to find the first tag matching `v[0-9]*vfs*` and build the git version number using that tag.
+
+Forking
+-------
+
+A personal fork of this repository and a branch in that repository should be used for development.
+
+These branches should be based on the latest vfs-# branch.  If there are work in progress pull requests that you have based on a previous version branch when a new version branch is created, you will need to move your patches to the new branch to get them in that latest version.
+
+#### Example
+```
+git clone <personal fork repo URL>
+git remote add ms https://github.com/Microsoft/git.git
+git checkout -b my-changes ms/vfs-2.20.0 --no-track
+git push -fu origin HEAD
+```