Add instructions

instructions.md

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+## How to demo
+
+Create a new codespace for actions/runner, then
+
+```bash
+git pull
+git checkout rentziass/dap
+```
+
+Then build the runner:
+
+```bash
+cd src && ./dev.sh layout && cd ..
+```
+
+Then register your runner (grab registration command from [here](https://github.com/organizations/galactic-potatoes/settings/actions/runners/new)):
+
+```bash
+cd _layout
+```
+
+```
+./config.sh --url <REPO_URL> --token <TOKEN> ## the command from above
+```
+
+Then start the runner:
+```bash
+./run.sh
+```
+
+### WebSocket Proxy
+
+In a new terminal we need to start the WebSocket proxy:
+
+```bash
+cd ./browser-ext && npm install && node proxy.js
+```
+
+After that starts, in VS Code we need to add the port forwarding for port `4712`
+(whereas the TCP DAP server will be on `4711`, but we don't need to forward that
+one).
+
+### Browser Extension
+
+For this I'd recommend cloning the repo (`gh repo clone actions/runner`) locally
+for simplicity, then loading the `browser-ext` folder as an unpacked extension
+in Chrome/Edge.
+
+### Debugging a job
+
+Now we want to re-run a failed job for [this workflow](https://github.com/galactic-potatoes/rentziass-test/actions/workflows/self-hosted.yaml) with debug logging enabled. **Once we're on the new job page** we can open the extension and connect. Upon successful connection we'll see steps appear, and clicking the `Debug` button will launch the debugger in page. If anything goes south with connection here simply cancelling the job allows to try again.