[A] Added CONTRIBUTING.md

CONTRIBUTING.md

@@ -0,0 +1,18 @@
+# How to contribute
+
+Here are a few guidelines that I hope will ease the process of contributing.
+
+## Files to change
+
+:exclamation: Before you make any changes, note that content of [`lib` directory](https://github.com/seleznevae/libfort/tree/develop/lib) is **generated** from the source files in the [`src` directory](https://github.com/seleznevae/libfort/tree/develop/src). Please **do not** edit files in `lib` directory directly, but change corresponding files in the `src` directory and regenerate files in the `lib` directory by executing `python amalgamate.py`.
+
+If you add or change a feature, please also add a unit test. The unit tests can be compiled and executed with
+
+   ```sh
+   $ mkdir build
+   $ cd build
+   $ cmake ..
+   $ cmake --build .
+   $ ctest
+   ```
+

README.md

@@ -5,7 +5,7 @@
 [![Build status](https://ci.appveyor.com/api/projects/status/ll1qygb56pho95xw/branch/master?svg=true)](https://ci.appveyor.com/project/seleznevae/libfort/branch/master)
 [![Build Status](https://cloud.drone.io/api/badges/seleznevae/libfort/status.svg?ref=/refs/heads/develop)](https://cloud.drone.io/seleznevae/libfort)
 [![Coverage Status](https://coveralls.io/repos/github/seleznevae/libfort/badge.svg?branch=master)](https://coveralls.io/github/seleznevae/libfort?branch=master)
-[![Try online](https://img.shields.io/badge/try-online-blue.svg)](https://wandbox.org/permlink/qQpqv3ujZ22ABVOz)
+[![Try online](https://img.shields.io/badge/try-online-blue.svg)](https://wandbox.org/permlink/oHLjXe8WmmKE3B1R)
 [![Documentation](https://img.shields.io/badge/docs-doxygen-blue.svg)](http://seleznevae.github.io/libfort)
 [![Doc](https://img.shields.io/badge/doc-wiki-blue.svg)](https://github.com/seleznevae/libfort/wiki)
 [![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://opensource.org/licenses/MIT)