General updates to satellite imagery labeling tool docs

[lsaloio]

Changes mostly involve grammar, wording, and formatting. Key changes include:

• Updated example image in the project builder that includes 'allow data import' option
• Breaking up 'steps' for the project builder into their own sections for a visually consistent read that is easier to follow
• Making important 'notes' or 'warnings' stand out visually by using block quote formatting so that users don't miss key information
• Bolding key words so that they stand out to readers and visually emphasize key parts of steps or concepts
• Adding a TOC in layers docs so users can navigate to specific layer instructions quickly
• Adding a link to layers docs in readme doc
• More specific/task-oriented headings to avoid confusion
• General fixes to typos and sentence structure to avoid confusion

[lsaloio]

@microsoft-github-policy-service agree company="UMass Amherst"

[calebrob6]

Great job Lauren, thanks a ton!

Note I really like the notes!

[rbrundritt]

Thanks Lauren!