cmd/tsconnect: add README with instructions

Outlines basic development, build and serving workflows.

Signed-off-by: Mihai Parparita <mihai@tailscale.com>

cmd/tsconnect/README.md

@@ -0,0 +1,30 @@
+# tsconnect
+
+The tsconnect command builds and serves the static site that is generated for
+the Tailscale Connect JS/WASM client.
+
+## Development
+
+To start the development server:
+
+```
+./tool/go run ./cmd/tsconnect dev
+```
+
+The site is served at http://localhost:9090/. JavaScript and CSS changes can be picked up with a browser reload. Go changes (including to the `wasm` package) require the server to be stopped and restarted. In development mode the state the Tailscale client is stored in `sessionStorage` and will thus survive page reloads (but not the tab being closed).
+
+## Deployment
+
+To build the static assets necessary for serving, run:
+
+```
+./tool/go run ./cmd/tsconnect build
+```
+
+To serve them, run:
+
+```
+./tool/go run ./cmd/tsconnect serve
+```
+
+By default the build output is placed in the `dist/` directory and embedded in the binary, but this can be controlled by the `-distdir` flag. The `-addr` flag controls the interface and port that the serve listens on.