Update doc for git layer

docs/layers/git.md

@@ -0,0 +1,37 @@
+---
+title: "SpaceVim git layer"
+---
+
+# [SpaceVim Layers:](https://spacevim.org/layers) git
+
+<!-- vim-markdown-toc GFM -->
+
+- [Description](#description)
+  - [Features](#features)
+- [Install](#install)
+  - [Layer](#layer)
+- [Key bindings](#key-bindings)
+
+<!-- vim-markdown-toc -->
+
+## Description
+
+This layers adds extensive support for [git](http://git-scm.com/).
+
+### Features
+
+## Install
+
+### Layer
+
+To use this configuration layer, add `call SpaceVim#layers#load('git')` to your custom configuration file.
+
+## Key bindings
+
+| Key Binding    | Description            |
+| -------------- | ---------------------- |
+| `<Leader> g a` | git add current file   |
+| `<Leader> g A` | git add All files      |
+| `<Leader> g b` | open git blame window  |
+| `<Leader> g s` | open git status window |
+| `<Leader> g c` | open git commit window |