Remove non-uswds style elements from template

[jimmyfagan]

Ticket

Resolves #18

Changes

These changes removed many of the custom style elements from the template. There was also a minor update to the readme file to help new users run the test script.

Context for reviewers

Details in #18; while these changes make the template look slightly less polished, the intention was to allow users of this template to use their own style elements, either from uswds or from their agency, without needing to pull out or overwrite custom style elements from the template.

Testing

Test Suites: 2 passed, 2 total
Tests:       4 passed, 4 total
Snapshots:   2 passed, 2 total
Time:        1.128 s
Ran all test suites.

Before:

After:

[jimmyfagan]

@sawyerh Since you wrote the issue, I'm putting you on review, so you can make sure this matches what you were expecting. If we need to add somebody else to get add'l feedback about this being okay, we can do that too. Thanks!