apidoc: footer: Make instructions clearer
# Help
To generate this documentation:
-```bash
+
+1. Install `Node.js` and `npm`
+2. Run:
+ ```console
git clone https://github.com/posativ/isso && cd isso
make apidoc-init apidoc
-$BROWSER apidoc/_output/index.html
+ ```
+3. View API documentation in browser at `./apidoc/_output/index.html`:
+ ```console
+ xdg-open apidoc/_output/index.html
```
