Add CONTRIBUTING.md file, remove changelog link in README and bump node

version for travis

Author: NicolasCARPi

.travis.yml

@@ -1,3 +1,3 @@
 language: node_js
 node_js:
-  - 6
+  - 12

CONTRIBUTING.md

@@ -0,0 +1,5 @@
+# Contributing to apidoc-core
+
+* Target the `dev` branch for your PR
+* Add a test if possible
+* Use `npm test`

README.md

@@ -1,11 +1,9 @@
 # apidoc-core
 
-Core parser library to generate apidoc result following the [apidoc-spec](https://github.com/apidoc/apidoc-spec)
+Core parser library to generate apidoc result following the [apidoc-spec](https://github.com/apidoc/apidoc-spec).
 
 [![Build Status](https://travis-ci.org/apidoc/apidoc-core.svg?branch=master)](https://travis-ci.org/apidoc/apidoc-core)
 [![Dependency Status](https://david-dm.org/apidoc/apidoc-core.svg)](https://david-dm.org/apidoc/apidoc-core)
 [![NPM version](https://badge.fury.io/js/apidoc-core.svg)](http://badge.fury.io/js/apidoc-core)
 
 If you are an end user, please proceed to [apidoc](https://github.com/apidoc/apidoc) or [apidoc-documentation](http://apidocjs.com).
-
-[Changelog](https://github.com/apidoc/apidoc/blob/master/CHANGELOG.md).