Add CONTRIBUTING.md and development.md (#56)

- Add the `CONTRIBUTING.md` document
- Add the `docs/development.md` document
- Add **Contributing** section to the main `README.md`
- Update `docs/README.md`'s table of contents
- Delete duplicate issue templates

CONTRIBUTING.md

@@ -0,0 +1,46 @@
+<h1>
+    <img alt="logo" src="./docs/assets/logo-small.png" width="28px" />
+    Codeowners Validator - contributing
+</h1>
+
+🎉🚀🤘 Thanks for your interest in the Codeowners Validator project! 🤘🚀🎉 
+
+This document contains contribution guidelines for this repository. Read it before you start contributing.
+
+## Contributing
+
+Before proposing or adding changes, check the [existing issues](https://github.com/mszostok/codeowners-validator/issues) and make sure the discussion/work has not already been started to avoid duplication. 
+
+If you'd like to see a new feature implemented, use this [feature request template](https://github.com/mszostok/codeowners-validator/issues/new?assignees=&labels=&template=feature_request.md) to create an issue. 
+
+Similarly, if you spot a bug, use this [bug report template](https://github.com/mszostok/codeowners-validator/issues/new?assignees=mszostok&labels=bug&template=bug_report.md) to let us know!
+
+### Ready for action? Start developing! 
+
+To start contributing, follow these steps: 
+
+1. Fork the `codeowners-validator` repository.
+
+2. Clone the repository locally. 
+
+    > **TIP:** This project uses Go modules, so you can check it out locally wherever you want. It doesn't need to be checked out in `$GOPATH`.
+
+3. Set the `codeowners-validator` repository as upstream:
+
+    ```bash
+    git remote add upstream git@github.com:mszostok/codeowners-validator.git
+    ```
+
+4. Fetch all the remote branches for this repository:
+
+    ```bash
+    git fetch --all 
+    ```
+
+5. Set the master branch to point to upstream:
+
+    ```bash
+    git branch -u upstream/master master
+    ```
+
+You're all set! 🚀  Read the [development](./docs/development.md) document for further instructions.

README.md

@@ -142,6 +142,10 @@ Application exits with different status codes which allow you to easily distingu
 | **2** | The application was closed because the OS sends a termination signal (SIGINT or SIGTERM). |
 | **3** | The CODEOWNERS validation failed - executed checks found some issues. |
 
+## Contributing
+
+Contributions are greatly appreciated! The project follows the typical GitHub pull request model. See [CONTRIBUTING.md](CONTRIBUTING.md) for more details.  
+
 ## Roadmap
 
 The [codeowners-validator roadmap uses Github milestones](https://github.com/mszostok/codeowners-validator/milestone/1) to track the progress of the project.

docs/README.md

@@ -5,6 +5,7 @@
 
 Welcome to the Codeowners Validator documentation.
 
++ [Development](./development.md)
 + [GitHub Action](./gh-action.md)
 + [GitHub personal access token](./gh-token.md)
 + [Release](./release.md)

docs/development.md

@@ -0,0 +1,88 @@
+[← back to docs](./README.md)
+
+# Development
+
+This document contains development instructions. Read it to learn how to develop this project.
+
+# Table of Contents
+
+<!-- toc -->
+
+- [Prerequisites](#prerequisites)
+- [Dependency management](#dependency-management)
+- [Testing](#testing)
+  * [Unit tests](#unit-tests)
+  * [Lint tests](#lint-tests)
+  * [Integration tests](#integration-tests)
+- [Build a binary](#build-a-binary)
+
+<!-- tocstop -->
+
+## Prerequisites
+
+* [Go](https://golang.org/dl/) 1.15 or higher
+* [Docker](https://www.docker.com/)
+* Make
+
+Helper scripts may introduce additional dependencies. However, all helper scripts support the `INSTALL_DEPS` environment variable flag.
+By default, this flag is set to `false`. This way, the scripts will try to use the tools installed on your local machine. This helps speed up the development process.
+If you do not want to install any additional tools, or you want to ensure reproducible script 
+results, export `INSTALL_DEPS=true`. This way, the proper tool version will be automatically installed and used. 
+
+## Dependency management
+
+This project uses `go modules` for dependency management. To install all required dependencies, use the following command:
+
+```bash
+go mod download
+```
+
+## Testing
+
+### Unit tests
+
+To run all unit tests, execute:
+
+```bash
+make test-unit
+```
+
+To generate the unit test coverage HTML report, execute: 
+
+```bash
+make test-unit-cover-html
+```
+
+> **NOTE:** The generated report opens automatically in your default browser.
+
+### Lint tests
+
+To check your code for errors, such as typos, wrong formatting, security issues, etc., execute:
+
+```bash
+make test-lint
+```
+
+To automatically fix detected lint issues, execute:
+
+```bash
+make fix-lint-issues
+```
+
+### Integration tests
+
+This project supports the integration tests that are defined in the [tests](../tests) package. The tests are executed against [`gh-codeowners/codeowners-samples`](https://github.com/gh-codeowners/codeowners-samples).
+
+> **CAUTION:** Currently, running the integration tests both on external PRs and locally by external contributors is not supported, as the teams used for testing are visible only to the organization members. 
+> At the moment, the `codeowners-validator` repository owner is responsible for running these tests. 
+
+## Build a binary
+
+To generate a binary for this project, execute:
+```bash
+make build
+```
+
+This command generates a binary named `codeowners-validator` in the root directory.
+
+[↑ Back to top](#table-of-contents)