update doc generation instructions to reflect new requirements.txt structure
# Updating the documentation
-First install the theme we use:
-```
-pip install -r requirements.txt
+First, if you haven't already, run:
+```bash
+cd ~/ParlAI; python setup.py develop
```
Then use make to build the html:
```
make html
```
+NOTE: Autodocs imports many agents, so you may run into `ImportError`s when running `make`. Just `pip install` as needed to continue.
Then, make any changes to the documentation in `source`, do `make html` again, and check your changes by checking the html files in `build/html` (you can start by opening `index.html`).
If everything looks good, make a Pull Request and the documentation will update automatically once the change has landed.
