docs: fix inaccurate readme claims and document bundle size

[duongdev]

Verified every claim against the published phosphor-react-native@3.0.6, the react-native-svg source, and tsc --strict --skipLibCheck false.

Tree-shaking claim (closes the README part of #61)

The README promised "Phosphor supports tree-shaking, so your bundle only includes code for the icons you use". Metro does not tree-shake by default, and the benchmark from #88 shows the barrel import costs +182% vs +10% for a direct import. Replaced with a Bundle size section carrying those numbers, plus the two real fixes: direct imports, or Expo's experimental tree-shaking.

Fixes

• Deep import path. phosphor-react-native/lib/commonjs/icons/Star is not in the exports map — it fails with ERR_PACKAGE_PATH_NOT_EXPORTED on any resolver honouring exports, which Metro does by default since RN 0.79. Removed; documented src/icons/* and its naming rule.
• TypeScript snippet did not compile. interface SvgProps extends DefaultSvgProps is self-recursive (TS2310) and DefaultIconProps was never imported (TS2304). Rewritten as plain module augmentation, with a note on why extends is wrong. Same bug fixed in global.d.ts.
• Props. Dropped "accepts all SVG props, including onClick" — IconProps is closed and RN has no onClick. Corrected the size-unit list: react-native-svg runs parseInt, so "2rem" is 2, not 32. Corrected duotoneColor, which falls back to color, not black. Added the missing style prop and per-prop defaults.
• Migrating from v2. Documents the Icon suffix, and that Circle / Path / Infinity have no deprecated alias (1509 of 1512 do).
• Context. Lists which props are context-able and their defaults.
• Related Projects. All eight repos have been renamed upstream (phosphor-react -> phosphor-icons/react, phosphor-icons -> web, and so on).
• Added badges, icon count, a Contributing section with the git submodule update --init --recursive step, and links to CONTRIBUTING.md and example/.

Verification

Every documented snippet typechecks against the published package under --strict with skipLibCheck: false — including size="50%", the duotone props, className after augmentation, and the src/icons/Star deep import. No formatting-only changes: the README was already not Prettier-clean on main, and yarn lint covers src/** only.

Noted, not fixed here

src/lib/icon-base.tsx:48-49 uses the raw weight prop instead of weight ?? contextWeight, so an icon rendered without an explicit weight gets testID="phosphor-react-native-star-undefined" and a matching className. Worth its own PR — I worded the README around it rather than documenting a wrong default.