Add READMEs to the npmjs packages

[tim-king-code-stuff]

Will appear here:

• https://www.npmjs.com/package/@bostonuniversity/burf-base?activeTab=readme
• https://www.npmjs.com/package/@bostonuniversity/burf-theme?activeTab=readme
• https://www.npmjs.com/package/@bostonuniversity/burf-tools?activeTab=readme
• https://www.npmjs.com/package/@bostonuniversity/burf-customizations?activeTab=readme