(docs): add a basic README

- Badges (tbd NPM package tho)
- Installation (also tbd NPM package)
- Usage and API
  - same format as mobx-persist and redux-persist, with a bit of
    copy+paste where exactly the same
- How it works encouraging looking under the hood
- Credits to redux-persist, mobx-persist, and the gist

README.md

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+# mst-persist
+
+[![package-json](https://img.shields.io/github/package-json/v/agilgur5/mst-persist.svg)](https://npmjs.org/package/mst-persist)
+[![releases](https://img.shields.io/github/release/agilgur5/mst-persist.svg)](https://github.com/agilgur5/mst-persist/releases)
+[![commits](https://img.shields.io/github/commits-since/agilgur5/mst-persist/latest.svg)](https://github.com/agilgur5/mst-persist/commits/master)
+
+[![dt](https://img.shields.io/npm/dt/mst-persist.svg)](https://npmjs.org/package/mst-persist)
+[![dy](https://img.shields.io/npm/dy/mst-persist.svg)](https://npmjs.org/package/mst-persist)
+[![dm](https://img.shields.io/npm/dm/mst-persist.svg)](https://npmjs.org/package/mst-persist)
+[![dw](https://img.shields.io/npm/dw/mst-persist.svg)](https://npmjs.org/package/mst-persist)
+
+[![NPM](https://nodei.co/npm/mst-persist.png?downloads=true&downloadRank=true&stars=true)](https://npmjs.org/package/mst-persist)
+
+Persist and hydrate MobX-state-tree stores.
+
+## Installation
+
+`npm i -S agilgur5/mst-persist`
+
+The `mst-persist` NPM package is not currently owned by me, so please install via GitHub for now.
+Will be looking to get ownership of the package [from the owner](https://github.com/pinqy520/mobx-persist/issues/37#issuecomment-361479253) shortly.
+
+## Usage
+
+```javascript
+import { types } from 'mobx-state-tree'
+import localForage from 'localForage'
+import { persist } from 'mst-persist'
+
+const SomeStore = types.model('Store', {
+  name: 'John Doe',
+  age: 32
+})
+
+const someStore = SomeStore.create()
+
+persist('some', someStore, {
+  storage: localForage,  // or AsyncStorage in react-native.
+                         // default: localStorage
+  jsonify: false  // if you use AsyncStorage, this shoud be true
+                  // default: true
+  whitelist: ['name']  // only these keys will be persisted
+}).then(() => console.log('someStore has been hydrated'))
+
+```
+
+### API
+
+#### `persist(key, store, options)`
+
+- arguments
+  - **key** *string* The key of your storage engine that you want to persist to.
+  - **store** *MST store* The store to be persisted.
+  - **options** *object* Additional configuration options.
+    - **storage** *[localForage](https://github.com/localForage/localForage) / AsyncStorage / localStorage* [localForage](https://github.com/localForage/localForage)-style storage API. localStorage for Web (default), AsyncStorage for React Native.
+    - **jsonify** *bool* Enables serialization as JSON (default: `true`).
+    - **whitelist** *Array\<string\>* Only these keys will be persisted (defaults to all keys).
+    - **blacklist** *Array\<string\>* These keys will not be persisted (defaults to all keys).
+
+- returns a void Promise
+
+## How it works
+
+Basically just a small wrapper around MST's `onSnapshot` and `applySnapshot`.
+The source code is currently shorter than this README, so take a look under the hood! :)
+
+## Credits
+
+Inspiration for parts of the code and API came from [`redux-persist`](https://github.com/rt2zz/redux-persist), [`mobx-persist`](https://github.com/pinqy520/mobx-persist), and [this MST persist PoC gist](https://gist.github.com/benjick/c48dd2db575e79c7b0b1043de4556ebc)