GH-50: Write the contributing guide (GH-53)

Author: ArtyomVancyan

CONTRIBUTING.md

@@ -0,0 +1,12 @@
+# Contributing to Thumbnails
+
+We welcome and appreciate your contributions to Thumbnails! In order to contribute to this repository, you must read the
+common [instructions](https://github.com/pysnippet/instructions#readme) of the PySnippet organization and follow the
+following guidelines:
+
+1. Fork the repository and create a new branch.
+2. Make and push your changes to the new branch.
+3. Create a pull request to the `master` branch of the repository.
+4. Wait for the pull request to be reviewed and merged.
+
+Thank you for your interest in contributing to Thumbnails. We look forward to working with you!

README.md

@@ -72,7 +72,7 @@ updates immediately. It will also install all the required dependencies listed i
 
 ## Contribute
 
-Everyone is welcome to contribute to this project. Please read and follow the [contribution guidelines](https://github.com/pysnippet/instructions#readme)
+Everyone is welcome to contribute to this project. Please read and follow the [contribution guidelines](CONTRIBUTING.md)
 before you start. Contributions can be considered:
 - Reporting an issue
 - Opening a pull-request