docs: readme explains how to run tests (conventional-changelog#3639)

Author: olets

.github/PULL_REQUEST_TEMPLATE.md

@@ -36,7 +36,7 @@ echo "your commit message here" | commitlint # fails/passes
 
 ## Checklist:
 
-<!--- Go over all the following points, and put an `x` in all the boxes that apply. -->
+<!--- Go over all the following points, and put an `x` in all the boxes that apply. See the README for information on testing. -->
 <!--- If you're unsure about any of these, don't hesitate to ask. We're here to help! -->
 
 - [ ] My change requires a change to the documentation.

README.md

@@ -31,6 +31,7 @@
 - [License](#license)
 - [Development](#development)
   - [Install and run](#install-and-run)
+  - [Testing](#testing)
   - [Publishing a release](#publishing-a-release)
 
 ---
@@ -254,6 +255,17 @@ yarn start # run tests, again on change
 
 For more information on how to contribute please take a look at our [contribution guide](./.github/CONTRIBUTING.md).
 
+### Testing
+
+From the project root directory, use the following commands to run the test suite
+
+```sh
+yarn clean
+yarn install
+yarn build
+yarn test
+```
+
 ### Package dependency overview
 
 ![commitlint-dependencies](https://user-images.githubusercontent.com/4248851/58385093-34b79780-7feb-11e9-8f27-bffc4aca3eba.png)