Update python layer documentation

docs/layers/lang/python.md

@@ -9,6 +9,16 @@ description: "This layer is for Python development, provide autocompletion, synt
 
 - [Description](#description)
 - [Features](#features)
+- [Install](#install)
+  - [Layer](#layer)
+  - [Syntax Checking](#syntax-checking)
+  - [Buffer formatting](#buffer-formatting)
+  - [Format imports](#format-imports)
+- [Key bindings](#key-bindings)
+  - [Inferior REPL process](#inferior-repl-process)
+  - [Running current script](#running-current-script)
+  - [Testing](#testing)
+  - [Refactoring](#refactoring)
 
 <!-- vim-markdown-toc -->
 
@@ -20,3 +30,63 @@ This layer is for Python development.
 
 - Aoto-completion using [deoplete-jedi](https://github.com/zchee/deoplete-jedi) or [jedi-vim](https://github.com/davidhalter/jedi-vim)
 - Documentation Lookup using [jedi-vim](https://github.com/davidhalter/jedi-vim)
+
+## Install
+
+### Layer
+
+To use this configuration layer, add `SPLayer 'lang#python'` to your custom configuration file.
+
+### Syntax Checking
+
+`checker` layer provide syntax checking feature, and for python it uses `flake8` package:
+
+```sh
+pip install --user flake8
+```
+
+### Buffer formatting
+
+The default key binding for formatting buffer is `SPC b f`, and you need to install `yapf`. To enable automatic buffer formatting on save, load this layer with setting `format-on-save` to `1`.
+
+```sh
+pip install --user yapf
+```
+
+### Format imports
+
+To be able to suppress unused imports easily, install [autoflake](https://github.com/myint/autoflake):
+
+```sh
+pip install --user autoflake
+```
+
+To be able to sort your imports, install [isort](https://github.com/timothycrosley/isort)
+
+```sh
+pip install --user isort
+```
+
+## Key bindings
+
+### Inferior REPL process
+
+Start a Python or iPython inferior REPL process with `SPC l s i`. If ipython is available in system executable search paths, ipython will be used to launch python shell; otherwise, default python interpreter will be used. You may change your system executable search path by activating a virtual environment.
+
+Send code to inferior process commands:
+
+| Key Binding | Description |
+| ----------- | ----------- |
+
+### Running current script
+
+To running a python script, you can press `SPC l r` to run current file without loss focus, and the result will be shown in a runner buffer.
+
+### Testing
+
+### Refactoring
+
+| Key Binding | Description                          |
+| ----------- | ------------------------------------ |
+| `SPC l r i` | remove unused imports with autoflake |
+| `SPC l r I` | sort imports with isort              |