docs: refresh README for the unified canvas + recent features

[vibhavkatre]

Updates the README to match where the product is now:

• One unified canvas section (Insert menu, in-frame editing, mixed document).
• Sharing (view/comment/edit + public), Desk app launcher, and optional Frappe Drive integration added to features.
• Frappe Cloud install section + an upgrade/rebuild note.
• Frappe Draw logo in the header.
• Notes the frontend now builds automatically on install (follows Fix: build the SPA on install so /draw isn't 'Page not found' #21).

Also updated the repo About description + topics via the GitHub API.

🤖 Generated with Claude Code

[greptile-apps]

Confidence Score: 4/5

Safe to merge after fixing the upgrade command — all other changes are accurate documentation.

The upgrade snippet instructs users to run bench get-app draw --branch main on an already-installed app, which will error out; only the one-line fix to bench update --app draw is needed before merging.

README.md — upgrade command block

_{Reviews (1): Last reviewed commit: "docs: refresh README for the unified can..." | Re-trigger Greptile}

[greptile-apps]

bench get-app installs a new app and will fail if the app is already present. The correct upgrade path is bench update --app draw (or cd apps/draw && git pull).

Suggested change

	> Upgrading an existing install? Pull the latest and rebuild the frontend:
	> ```bash
	> bench get-app draw --branch main
	> bench build --app draw && bench --site your-site.localhost clear-cache
	> ```
	> Upgrading an existing install? Pull the latest and rebuild the frontend:
	> ```bash
	> bench update --app draw
	> bench build --app draw && bench --site your-site.localhost clear-cache
	> ```

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!