Updating the introduction.

[snekkenull]

Context

What is the purpose of this PR? Is it to

• add a new feature
• fix a bug
• update tests and/or documentation
• other (please add here)

Please link to any issues this PR addresses.
comment

Changelog

• Correct the expression and add a description of the advanced options for app.
• Add webui in main README and link to app dicectory.

Test plan

Please make sure to do each of the following if applicable to your PR. (If you're not sure about any one of these just ask and we will happily help.)

• run pre-commit hooks and linters (make sure you've first installed via pre-commit install)
• add unit tests for any new functionality
• update docstrings for any new or updated methods or classes
• run unit tests via pytest tests
• include relevant commands and any other artifacts in this summary (eval results, etc.)