Add all files and readme

[dividing-by-zaro]

In this PR

• Add two folders: planning and milestones
• Update README.md to include public-facing info about the project (name, description, demo, deployed link, etc.)
• Within the planning folder, each deliverable includes a separate file for students to complete
• Within the milestones folder, each unit corresponds to a Milestone, which has a checklist students can use to make sure they've completed everything and a brief reflection section based on the reflection questions included in SITE

[dividing-by-zaro]

@karencarreon In each milestone, students will be checking off completed features and adding a GIF that shows that feature in action. I felt it made more sense to have that tied to the main readme.md rather than feature_list.md, so students can show off their overarching progress rather than having it buried in the planning section. I think it will also streamline grading.

[dividing-by-zaro]

@karencarreon At this point, all milestone checklists and planning files should be complete.