Add fetchStore docs

Author: techniq

sites/docs/src/routes/docs/svelte-stores/fetchStore/+page.md

@@ -1,13 +1,79 @@
 <script lang="ts">
 	import Preview from '$docs/Preview.svelte';
-
 	import fetchStore from '$svelte-stores/fetchStore';
-
-  // const { loading, data, error } = fetchStore(/*...*/)
 </script>
 
 <h1>Usage</h1>
 
 ```js
-import { fetchStore } from '@layerstack/svelte-stores';
+import { fetchStore, initFetchClient } from '@layerstack/svelte-stores';
+
+const state = fetchStore();
+
+// Request new data
+state.fetch(url, options?)
+
+// Re-fetch last request (same url and options)
+state.refresh();
+
+// Clear data
+state.clear();
+
+// Request inflight
+$state.loading
+
+// Data (success)
+$state.data
+
+// Error (failure)
+$state.error
+
+// Fetch options
+state.fetch(url, {
+	as: 'auto' // 'auto' (default, determined by response `Content-Type`) | 'arrayBuffer' | 'blob' | 'formData' | 'json' | 'text'
+})
+
+// Disable fetching (control externally)
+state.fetch(url, {
+	disabled: isDisabled
+})
+
+// Force re-fetch even if data exists for current url (ignore cache)
+state.fetch(url, {
+	force: true
+})
+
+// Only fetch once (unless `force: true` is also set)
+state.fetch(url, {
+	once: true
+})
+
+// Transform data before updating `$state.data`
+state.fetch(url, {
+	onDataChange: (newData, currentData) => {
+		// Useful to concat to existing data, transform data, etc.
+		return newData;
+	},
+})
+
+// Evaluate response
+state.fetch(url, {
+	onResponseChange: (response, data) => {
+		// Useful to check `response.ok` or `response.status`,
+		// refresh another fetch (ex. GET) after mutation (POST, PUT, PATCH, DELETE), etc
+		// If value returned, will update `$state.data`
+	},
+})
+
+// Initialize fetch client with global options (context, typically set in `+layout.svelte`)
+initFetchClient({
+	// Useful to set global headers such as `Authorization`
+	options: () => {
+		return {
+			headers: {
+				Authorization: `Bearer ${accessToken}`
+			}
+		};
+	},
+})
 ```