Create unsplash.md (#629)

Author: siddsarkar

docs/config-examples/unsplash.md

@@ -0,0 +1,27 @@
+# Unsplash
+
+If you don't already have a unsplash app, create it [here](https://unsplash.com/oauth/applications).
+
+Once you have an app, go to your app page. Here you'll need to add two things:
+
+1. Redirect URL
+   Under "Redirect URLs", add one for your app, e.g. `com.myapp://oauth` and save
+
+2. Scopes
+   Under "Scopes", add the scopes you want to request from the user, e.g, "public"
+
+```js
+const config = {
+  usePKCE: false, // Important !!
+  clientId: '<client_id>', // found under App Credentials
+  clientSecret: '<client_secret>', // found under App Credentials
+  scopes: ['public'], // choose any of the scopes set up in step 1
+  redirectUrl: 'com.myapp://oauth', // set up in step 2
+  serviceConfiguration: {
+    authorizationEndpoint: 'https://unsplash.com/oauth/authorize',
+    tokenEndpoint: 'https://unsplash.com/oauth/token',
+  },
+};
+
+const authState = await authorize(config);
+```