docs: Add API usage on README

README.md

@@ -7,3 +7,69 @@ If you find this useful, please consider supporting my work with a [donation](ht
 ## Description
 
 A utility for posting across multiple social networks at once.
+
+## Installation
+
+```shell
+npm install @humanwhocodes/crosspost
+```
+
+## Usage
+
+### API Usage
+
+The API is split into two parts:
+
+1. The `Client` class that can be used to post the same message across multiple services.
+1. A number of different strategy implementations, one for each service:
+    * `BlueskyStrategy`
+    * `MastodonStrategy`
+    * `TwitterStrategy`
+
+Each strategy requires its own parameters that are specific to the service. If you only want to post to a particular service, you can just directly use the strategy for that service.
+
+```js
+import {
+    Client,
+    TwitterStrategy,
+    MastodonStrategy,
+    BlueskyStrategy
+} from "@humanwhocodes/crosspost";
+
+// Note: Use an app password, not your login password!
+const bluesky = new BlueskyStrategy({
+    identifier: "me.you.social",
+    password: "your-app-password",
+    host: "you.social"
+})
+
+// Note: Personal access token is required
+const mastodon = new MastodonStrategy({
+    accessToken: "your-access-token",
+    host: "mastodon.host"
+});
+
+// Note: OAuth app is required
+const twitter = new TwitterStrategy({
+    accessTokenKey: "access-token-key",
+    accessTokenSecret: "access-token-secret",
+    apiConsumerKey: "api-consumer-key",
+    apiConsumerSecret: "api-consumer-secret"
+});
+
+// create a client that will post to all three
+const client = new Client({
+    strategies: [
+        bluesky,
+        mastodon,
+        twitter
+    ]
+});
+
+// post to all three
+await client.post("Hello world!");
+```
+
+## License
+
+Apache 2.0