The section about contributing to the project added to documentation.

README.md

@@ -39,6 +39,61 @@ the [General Decimal Arithmetic](http://speleotrove.com/decimal/) specification.
 
 `decimal` only explicitly supports the two most recent major Go 1.X versions.
 
+## Contributing to `decimal`
+
+We welcome contributions to `decimal` of any kinds including bug reports, issues, feature requests, PRs to documentation, feature implementations and bug fixes.
+
+### Code contribution
+
+To make a contribution do the following:
+
+* Fork the project, start new branch and make your changes
+* Make test cases for the new code
+* Do not forget to run `go fmt`
+* Add or update documentation if you are adding new features or changing functionality
+* Provide a good commit message with the reference to a closed issue if any
+
+### Testing the code
+
+There are 4 main types of tests:
+
+1. Python-generated test tables. Python 3 is used to generate test tables that are parsed using the `suite` package. 
+2. `dectest` tables. The `dectest` tables are similar to Python tables. They are parsed using `dectest` package. 
+3. Custom tests. The custom tests are strewn thought the different *_test.go files.
+4. Bug-specific  tests. They are placed inside `issues_test.go` file. 
+
+#### Generating test data
+
+Before running the tests test data have to be generated. 
+
+To generate Python test tables run the following commands inside the project's directory:
+
+```
+cd testdata/pytables
+./tables.py 500
+cd ../..
+```
+
+To generate `dectest` data execute the command:
+
+```
+testdata/dectest/generate.bash
+```
+
+#### Running the test cases
+
+To run the full test suite execute the following command. Please, note that the timeout for tests increased to 30 minutes. 
+
+```
+go test -timeout 30m -v
+```
+
+Some test could take a long time, use `-short` flag to run only quick tests.
+
+```
+go test -short -v
+```
+
 ## License
 
 [BSD 3-clause](https://github.com/ericlagergren/decimal/blob/master/LICENSE)