docs: add docs

Author: posva

README.md

@@ -1,6 +1,8 @@
 # vue-compose-promise [![Build Status](https://badgen.net/circleci/github/posva/vue-compose-promise)](https://circleci.com/gh/posva/vue-compose-promise) [![npm package](https://badgen.net/npm/v/vue-compose-promise)](https://www.npmjs.com/package/vue-compose-promise) [![coverage](https://badgen.net/codecov/c/github/posva/vue-compose-promise)](https://codecov.io/github/posva/vue-compose-promise) [![thanks](https://badgen.net/badge/thanks/♥/pink)](https://github.com/posva/thanks)
 
-> Some awesome description
+> Easily manipulate Promises and their state in Vue
+
+**Depends on [@vue/composition-api](https://github.com/vuejs/composition-api)**
 
 Demo (TODO link)
 
@@ -12,10 +14,51 @@ npm install vue-compose-promise
 
 ## Usage
 
+```vue
+<template>
+  <div>
+    <span> Is the promise still pending: {{ usersPromise.isPending }} </span>
+    <span> Is the 200ms delay over: {{ usersPromise.isDelayOver }} </span>
+    <span>
+      Last succesfully resolved data from the promise: {{ usersPromise.data }}
+    </span>
+    <span> Error if current promise failed: {{ usersPromise.error }} </span>
+  </div>
+</template>
+
+<script>
+import { createComponent } from '@vue/composition-api'
+import { usePromise } from 'vue-compose-promise'
+
+export default createComponent({
+  setup() {
+    const promised = usePromise({ pendingDelay: 200, promise: fetchUsers() })
+
+    return {
+      usersPromise: promised.state,
+
+      fetchUsers() {
+        promised.state.promise = fetchUsers()
+      },
+    }
+  },
+})
+</script>
+```
+
 ## API
 
+### `usePromise<T>(options?: { pendingDelay?: number | Ref<number>; promise?: Promise<T> | Ref<Promise<T>> })`
+
+- `options`
+  - `pendingDelay`: amount of time in _ms_ that should be wait whenever the a new promise is pending. This allows delaying the display of a loader to avoid flashing the screen. Can be a _reactive_ property.
+  - `promise`: initial promise. Can be null. Can be a _reactive_ property.
+
 ## Related
 
+- [vue-promised](https://github.com/posva/vue-promised)
+- [@vue/composition-api](https://github.com/vuejs/composition-api)
+
 ## License
 
 [MIT](http://opensource.org/licenses/MIT)