Add instructions and example code for basic SDK usage

doc/SDK.md

@@ -0,0 +1,77 @@
+# How to use Hydrogen as an SDK
+
+If you want to use end-to-end encryption, it is recommended to use a [supported build system](../src/sdk/paths/) (currently only vite) to be able to locate the olm library files.
+
+You can create a project using the following commands
+
+```sh
+# you can pick "vanilla-ts" here for project type if you're not using react or vue
+yarn create vite
+cd <your-project-name>
+yarn
+yarn add https://github.com/vector-im/hydrogen-web.git
+```
+
+If you go into the `src` directory, you should see a `main.ts` file. If you put this code in there, you should see a basic timeline after login and initial sync have finished.
+
+```ts
+import {
+    Platform,
+    SessionContainer,
+    LoadStatus,
+    createNavigation,
+    createRouter,
+    RoomViewModel,
+    TimelineView
+} from "hydrogen-web";
+import {olmPaths, downloadSandboxPath} from "hydrogen-web/src/sdk/paths/vite";
+
+const app = document.querySelector<HTMLDivElement>('#app')!
+
+// bootstrap a session container
+const platform = new Platform(app, {
+    downloadSandbox: downloadSandboxPath,
+    olm: olmPaths,
+}, null, { development: true });
+const navigation = createNavigation();
+platform.setNavigation(navigation);
+const urlRouter = createRouter({
+    navigation: navigation,
+    history: platform.history
+});
+urlRouter.attach();
+const sessionContainer = new SessionContainer({
+    platform,
+    olmPromise: platform.loadOlm(),
+    workerPromise: platform.loadOlmWorker()
+});
+
+// wait for login and first sync to finish
+const loginOptions = await sessionContainer.queryLogin("matrix.org").result;
+sessionContainer.startWithLogin(loginOptions.password("bruno4", "testtest"));
+await sessionContainer.loadStatus.waitFor((status: string) => {
+    return status === LoadStatus.Ready ||
+        status === LoadStatus.Error ||
+        status === LoadStatus.LoginFailed;
+}).promise;
+// check the result
+if (sessionContainer.loginFailure) {
+    alert("login failed: " + sessionContainer.loginFailure);
+} else if (sessionContainer.loadError) {
+    alert("load failed: " + sessionContainer.loadError.message);
+} else {
+    // we're logged in, we can access the room now
+    const {session} = sessionContainer;
+    const room = session.rooms.get("!bEWtlqtDwCLFIAKAcv:matrix.org");
+    const vm = new RoomViewModel({
+        room,
+        ownUserId: session.userId,
+        platform,
+        urlCreator: urlRouter,
+        navigation,
+    });
+    await vm.load();
+    const view = new TimelineView(vm.timelineViewModel);
+    app.appendChild(view.mount());
+}
+```