Add contributing.md (Strobotti#5)

Author: Strobotti

CONTRIBUTING.md

@@ -0,0 +1,49 @@
+# Contributing to php-jwk
+
+This is a very small library with a very limited scope but if you want to contribute please feel free to do so.
+
+## How can I contribute?
+
+### Reporting bugs
+
+You can open [a new issue](https://github.com/Strobotti/php-jwk/issues) once you have checked one covering your issue hasn't been opened yet.
+
+### Open a pull-request
+
+If you want to fix a bug or add a missing feature you can open a new pull-request.
+
+Please note that you need a PHP 7.2 or later for using this library (including running the tests).
+
+Basic steps:
+
+1. Fork this repository
+1. Clone it locally
+1. Install dependencies with Composer
+    ```bash
+    composer install
+    ```
+1. Create a branch on your fork
+1. Commit & push
+1. Open a pull-request from your branch
+1. Profit
+
+Some guidelines:
+
+1. Before committing make sure to format the code accordingly:
+    ```bash
+    make php-cs-fixer-fix
+    ```
+1. Also make sure the tests pass successfully and you have sufficient coverage
+    ```bash
+    make test-unit
+    ```
+
+### Git Commit Messages
+
+* Use the present tense ("Add feature" not "Added feature")
+* Use the imperative mood ("Move cursor to..." not "Moves cursor to...")
+* Limit the first line to 72 characters or less
+
+## License
+
+[MIT](https://github.com/Strobotti/php-jwk/blob/master/LICENSE)

README.md

@@ -1,5 +1,6 @@
 # php-jwk
 
+[![Build Status](https://travis-ci.com/Strobotti/php-jwk.svg?branch=master)](https://travis-ci.com/Strobotti/php-jwk)
 [![codecov](https://codecov.io/gh/Strobotti/php-jwk/branch/master/graph/badge.svg)](https://codecov.io/gh/Strobotti/php-jwk)
 
 A small PHP library to handle JWKs (Json Web Keys)
@@ -120,3 +121,7 @@ lq2ybzcLh3zyhCitBOebiRWDQfG26EH9lTlJhll+p/Dg8vAXxJLIJ4SNLcqgFeZe
 xwIDAQAB
 -----END PUBLIC KEY-----
 ```
+
+### Contributing
+
+See [CONTRIBUTING.md](CONTRIBUTING.md) for more details.