Update README adding Contributing section.

* Add Contributing section including Testing sub section.
* Change the repository name's heading level.
  Replace the heading level 2 syntax ("--") with the more popular heading level
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README.md

@@ -1,5 +1,4 @@
-Shared ruby tests
------------------
+# Shared ruby tests
 
 This repository contains shared ruby tests.
 
@@ -8,3 +7,31 @@ Available integration tests:
  * systemtap-static-probes-in-ruby - exercising ruby's systemtap api
  * bundler-unit-test - run bundler's unit tests
  * run-basic-rails-application - run a simple rails application
+
+## Contributing
+
+### Testing
+
+You can run the tests in your local environment.
+
+Install [`tmt`](https://tmt.readthedocs.io/en/stable/overview.html#install).
+
+```
+$ sudo dnf install tmt+all
+```
+
+Run the following command to run the tests for Fedora rawhide:
+
+```
+$ tmt -c distro=fedora-rawhide run --all provision -h virtual -i fedora-rawhide plans --default
+/var/tmp/tmt/run-NNN
+...
+```
+
+The tmt's provisioning method virtual (`tmt run provision -h virtual`) must be used, otherwise the tests fail due to known issues with container provisioning method (`tmt run provision -h container`). Also note the `run-NNN` printed on the output of the command. This represents the run ID used with `tmt run --id` option in later steps.
+
+Run the following command to see the report, setting the value of the above run ID to the `--id` option. As this repository doesn't have tmt's plans to run the tests, we need to set the `plans --default` to use the default plans. See [this tmt's document](https://tmt.readthedocs.io/en/stable/stories/cli.html#report) about the `tmt run report` options.
+
+```
+$ tmt run --id run-NNN report -vvv plans --default
+```