Some copyediting and suggestions

Things of note:

- I'm proposing the removal of the "Public domain" section at the bottom of CONTRIBUTING, as it seems redundant to the first paragraph of that file.
- I added a note to step 4 in the README to remove the "Exceptions" section in TERMS if it is not needed.
- In the README, under "Open source licensing info", I swapped the order of TERMS and LICENSE, because TERMS is what provides the broader context.

Let me know if you disagree with any of these suggestions.