improvements for START book chair guide

Hello again!

The [START guide](https://github.com/acl-org/ACLPUB/blob/master/docs/start.md) doesn't mention the files `just-program.tex` and `just-toc.tex`, however, without them compiling proceedings on START is not possible. Also, START interface (Templates tab) has no fields for those two files. So in my understanding, the [Step 3](https://github.com/acl-org/ACLPUB/blob/master/docs/start.md#step-3--dwnl-templates-tab) of the guide becomes an obligatory one contrary to what is stated there.

I'd issue a PR to fix that, but I'm not sure if my understanding is correct, and if there wouldn't be any changes planned to templates and/or START interface.

Thank you for all your work!