Small README changes

[rwegener2]

This PR makes two small suggestions to the README:

1. Fixes a typo
2. Adds description of how to run tests

For the tests description of course please re-write, move to another section, or change as you see fit (you should have edit access to this branch). Just wanted to put in a placeholder.

openjournals/joss-reviews#7406

[rwegener2]

Line 83 is really interesting, but I worry it is a bit dense for someone with less programming background. I would consider adding some higher level text before the denser paragraph, for example maybe
"NdbcApi provides a singular access point for NDBC data. All the methods for finding data, metadata, and locating stations are available using the api object."

[CDJellen]

Thank you for this suggestion; I agree and have included this change in the PR you opened.

While I enjoyed building these features when initially designing the API, they are all but irrelevant to end users.

Additionally, I've split off the test instructions into a new CONTRIBUTING.md guide.

[rwegener2]

One more comment -- I found it took a moment to understanding "modes". I will suggest a more thorough explanation of modes in the example notebook, but 1-2 short sentences explaining that data variables are grouped into modes here in the README may also be helpful.

[CDJellen]

One more comment -- I found it took a moment to understanding "modes". I will suggest a more thorough explanation of modes in the example notebook, but 1-2 short sentences explaining that data variables are grouped into modes here in the README may also be helpful.

Thank you for pointing this out; I've made some updates to the README to contextualize each of the mode identifiers.