docs: update README

Author: hassy

README.md

@@ -1,2 +1,44 @@
 # Running Artillery tests in parallel with GitHub Actions
 
+This is an example showing how you can run multiple Artillery load tests in parallel on GitHub Actions with the [matrix strategy](https://docs.github.com/en/actions/writing-workflows/choosing-what-your-workflow-does/running-variations-of-jobs-in-a-workflow).
+
+## Code structure
+
+1. The main Artillery configuration file is in [`config.yml`](./config.yml). This defines our target and load phases. In a more realistic test it would also include plugin configuration, load custom JS/TS code, etc.
+2. We have 3 different VU scenarios defined in files under `scenarios`, e.g. [`scenarios/armadillo.yml`](./scenarios/armadillo.yml).
+
+Our goal is to run 3 Artillery load tests in parallel, using the config file with each individual scenario file.
+
+## GitHub Actions workflow
+
+Our workflow definition is in [`.github/workflows/run-artillery-tests.yml`](./.github/workflows/run-artillery-tests.yml).
+
+To run 3 Artillery load tests in parallel we define a matrix containing the names of our scenarios:
+
+```yaml
+matrix:
+  # Create a scenario_name variable in this job that will be used to
+  # run an Artillery test for that scenario
+  scenario_name:
+    - armadillo
+    - dino
+    - pony
+```
+
+That creates a `scenario_name` variable in the workflow which we can use to run an Artillery load test as a GitHub Actions job:
+
+```yaml
+- name: Run Artillery tests in parallel
+  run: |
+    artillery run scenarios/${{matrix.scenario_name}}.yml --config config.yml
+```
+
+GitHub Actions will automatically create a job for each option we define in the matrix. The end result looks like this:
+
+3 jobs running in parallel, one for each scenario:
+
+![checks](./images/checks.png)
+
+The workflow view in the **Actions** tab:
+
+![ui](./images/jobs.png)