README.md

[nicole-brewer]

• Revisit motivation. Edit or redo [Namita: 15 min, David: 45 min, 45 min] #22
• A list of extensions and other IDE-like features
• One line about what each extension does [20, 45, 45] #23
• Test usage instructions and update if needed [30, 1 hour, 4 hours] #24