Add section of 'File detection'

README.md

@@ -4,7 +4,7 @@ requirements.txt.vim
 [![Build Status](https://travis-ci.org/raimon49/requirements.txt.vim.svg?branch=master)](https://travis-ci.org/raimon49/requirements.txt.vim)
 [![Dependency Status](https://gemnasium.com/raimon49/requirements.txt.vim.svg)](https://gemnasium.com/raimon49/requirements.txt.vim)
 
-[the Requirements File Format](http://pip.readthedocs.org/en/stable/reference/pip_install/#requirements-file-format) syntax support for Vim
+[the Requirements File Format](http://pip.readthedocs.org/en/stable/reference/pip_install/#requirements-file-format) syntax support for Vim.
 
 ![requirements txt-sc](https://cloud.githubusercontent.com/assets/221802/11379923/5cbb4862-9336-11e5-8963-217b2d7df397.png)
 
@@ -36,6 +36,31 @@ $ git clone https://github.com/raimon49/requirements.txt.vim.git ~/.vim/bundle/r
 
 Deploy all files under `$VIMRUNTIME`
 
+File detection
+--------------
+
+`requirements.txt.vim` detects filename automatically.
+
+* `requirements.txt`
+* `dev-requirements.txt`
+* `requirements/dev.txt`
+* `requires/tests.txt`
+* `requirements.in`
+    * Use for [pip-tools](https://github.com/nvie/pip-tools) (a.k.a. Better dependency management tool).
+
+If you want to customize it.
+
+```vim
+" Add 'freeze' to your .vimrc as a detection pattern
+let g:requirements#detect_filename_pattern = 'freeze'
+```
+
+```sh
+$ pip freeze > my-freeze.txt
+# You can edit it as a 'Requirements File Format'
+$ vim my-freeze.txt
+```
+
 License
 -------