Draft of README content of new polyfill repo (#1)

* Draft of README content of new repo

* Updates from @ptomato review feedback

Author: justingrant

README.md

@@ -1 +1,73 @@
 # Temporal Polyfill
+
+## Polyfill for [TC39 Proposal: Temporal](https://github.com/tc39/proposal-temporal)
+
+This polyfill was kicked off by some of the champions of the [Temporal proposal](https://github.com/tc39/proposal-temporal).
+The goal is to be ready for production use when the Temporal proposal reaches Stage 4, although like with all OSS work progress is dependent on contributors.
+We're eagerly welcoming to contributors who want to help build and maintain this polyfill.
+PRs are always welcome!
+
+Note that this polyfill is not affiliated with TC39. Links to other polyfills can be found [here](https://github.com/tc39/proposal-temporal/tree/main/#polyfill).
+
+This polyfill is compatible with Node.js 14 or later.
+
+## Roadmap
+
+* [x] Fork non-production polyfill from [tc39/proposal-temporal repo](https://github.com/tc39/proposal-temporal/tree/main/polyfill)
+* [x] Release initial pre-alpha to NPM at [@js-temporal/polyfill](https://www.npmjs.com/package/@js-temporal/polyfill)
+* [ ] Sync the code in this repo with the handful of polyfill changes that have recently been made in the [tc39/proposal-temporal](https://github.com/tc39/proposal-temporal) repo
+* [ ] Release alpha version to NPM 
+* [ ] Deprecate all other earlier Temporal polyfills
+* [ ] Convert to TypeScript for better maintainability
+* [ ] (Maybe) Optimize performance of slow operations, notably non-ISO calendar calculations
+* [ ] Release production version to NPM
+
+## Bug Reports and Feedback
+
+If you think you've found a bug in the Temporal API itself (not the implementation in this polyfill), please file an issue in the [tc39/proposal-temporal issue tracker](https://github.com/tc39/proposal-temporal/issues) issue tracker.
+
+If you've found a bug in this polyfill—meaning that the implementation here doesn't match the [Temporal spec](https://tc39.es/proposal-temporal/)—please file an issue in this repo's [issue tracker](https://github.com/js-temporal/temporal-polyfill/issues).
+
+## Documentation
+
+Reference documentation and examples for the Temporal API can be found [here](https://tc39.es/proposal-temporal/docs/index.html).
+
+A cookbook to help you get started and learn the ins and outs of Temporal is available [here](https://tc39.es/proposal-temporal/docs/index.html)
+
+If you find a bug in the documentation, please file a bug over in the [tc39/proposal-temporal issue tracker](https://github.com/tc39/proposal-temporal/issues) issue tracker.
+
+Note that the Temporal documentation is in the process of being migrated to [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript).
+You can track the progress of the MDN migration [here](https://github.com/tc39/proposal-temporal/issues/1449).
+
+## Usage
+
+To install:
+
+```bash
+$ npm install @js-temporal/polyfill
+```
+
+CJS Usage:
+
+```javascript
+const { Temporal, Intl, toTemporalInstant } = require('@js-temporal/polyfill');
+Date.prototype.toTemporalInstant = toTemporalInstant;
+```
+
+Import the polyfill as an ES6 module:
+
+```javascript
+import { Temporal, Intl, toTemporalInstant } from '@js-temporal/polyfill/lib/index.mjs';
+Date.prototype.toTemporalInstant = toTemporalInstant;
+```
+
+Note that this polyfill currently does not install a global `Temporal` object like a real implementation will.
+This behavior avoids hiding the global Temporal object in environments where a real Temporal implementation is present.
+See [this issue](https://github.com/tc39/proposal-temporal/issues/778) for more background on this decision.
+Once JS engines start shipping with Temporal, we may decide to change this behavior to match built-in behavior more closely.
+See [#2](https://github.com/js-temporal/temporal-polyfill/issues/2) to provide feedback or track this issue.
+
+## Contributing / Help Wanted
+
+We're eagerly welcoming to contributors who want to help build and maintain this polyfill.
+PRs are always welcome!