docs: README.md and manifest.webmanifest still describe StudyMap as Mumbai-only

[yakew7]

Problem

The CHANGELOG.md [Unreleased] section already records this exact fix having been done once:

lib/site.ts and /about no longer claim Mumbai-only coverage now that the dataset is global

Confirmed — both are clean today:

$ grep -n "tagline" src/lib/site.ts
3:  tagline: "Find student places and perks in cities worldwide.",
$ grep -n "worldwide" src/app/about/page.tsx
20:    body: "...in one place across cities worldwide. No login, no app to install.",

But two more places carrying the same stale claim survived that pass:

README.md line 3 (the opening tagline, right above a bullet on line 28 that correctly says otherwise):

A crowdsourced map of student-important places across the Mumbai Metropolitan Region (Mumbai, Thane, Navi Mumbai). Open source, zero setup, free forever.

public/manifest.webmanifest (shown to users in the browser's "Install app" prompt):

"screenshots": [
  {
    "src": "/brand/og.png",
    ...
    "label": "StudyMap — resource map for Mumbai"
  }
]

The manifest's top-level description also lists categories that don't match the app's actual place types (mentions "stationery shops", which isn't one of the 6 real categories, while omitting "government offices" and "airports," which are):

"description": "Crowdsourced study resource map for students worldwide. Find libraries, exam centres, stationery shops, and more."

The dataset spans 371 cities in sat_centre.json alone across more than a dozen countries (India, US, UK, Turkey, UAE, South Korea, Nigeria, Kenya, South Africa, Spain, Germany, France, Canada, Australia, Singapore), so both of these visibly undersell/misdescribe the product to a new visitor or installer.

Fix

• README.md line 3: rewrite to match the accurate framing already used in site.ts//about (student places worldwide, not Mumbai-only).
• public/manifest.webmanifest: fix the screenshot label, and update description to name the app's actual 6 place categories (or a subset) instead of "stationery shops".

Acceptance criteria

• README.md's opening line matches the global scope described in the rest of the file
• manifest.webmanifest's label and description no longer claim Mumbai-only scope or list a non-existent category