Added contribution guidelines

CONTRIBUTING.md

@@ -0,0 +1,25 @@
+# How to contribute
+
+## Building
+
+Use `dotnet build` to build.
+
+## Testing
+
+Use `dotnet test` to run tests. At the moment the tests are end-to-end UI tests that use [Selenium.WebDriver](https://www.nuget.org/packages/Selenium.WebDriver) to operate a test application, running FlaUI.WebDriver.exe in the background, so they should be run on Windows.
+
+Add UI tests for every feature added and every bug fixed, and feel free to improve existing test coverage.
+
+## Submitting changes
+
+Please send a [GitHub Pull Request](https://github.com/FlaUI/FlaUI.WebDriver/pulls) with a clear list of what you've done (read more about [pull requests](http://help.github.com/pull-requests/)). Please follow our coding conventions (below) and make sure all of your commits are atomic (one feature per commit).
+
+Always write a clear log message for your commits. One-line messages are fine for small changes, but bigger changes should look like this:
+
+    $ git commit -m "A brief summary of the commit
+    > 
+    > A paragraph describing what changed and its impact."
+
+## Coding conventions
+
+Follow the [.NET Runtime Coding Style](https://github.com/dotnet/runtime/blob/main/docs/coding-guidelines/coding-style.md).