WIP: Add core-loader docs

packages/core-loader/README.md

@@ -8,6 +8,55 @@
 ```sh
 npm install @sanity/core-loader @sanity/client
 ```
+core-loader uses [nanostores](https://github.com/nanostores/nanostores) to poll a Sanity Studio for changes and expose those changes via a listener.
+
+## createQueryStore
+`createQueryStore` initializes the loader, it takes 3 arguments:
+* `client` - An initialized Sanity client
+* `ssr` - Optional (defaults to `false`): Boolean to flag if you plan to fetch production data on the server
+* `tag` - Optional (defaults to `core-loader`): An ID for API request logs to easily determine the source of API traffic
+
+```javascript
+const queryStore = createQueryStore({
+    client,
+})
+```
+
+Once initialized, createQueryStore exposes 3 methods
+### createFetcherStore
+`createFetcherStore` fetches a given query and (when `liveMode` is enabled) re-fetches as changes are made in the Studio, it takes 3 arguments:
+* query - A GROQ query
+* params - Optional object of parameters for the query
+* initial - If using SSR, the initial server-fetched data 
+
+```javascript
+const fetcherStore = queryStore.createFetcherStore(query, {}, initial) 
+```
+
+Once initialized `createFetcherStore` provides a `subscribe` function that returns the query response and when combined with `enableLiveMode` will allow for live visual editing.
+```javascript
+// Listen for changes + re-render HTML in response
+fetcherStore.subscribe(({loading, data}) => {
+    if (!loading && data) {
+        renderHtml(data)
+    }
+})
+```
+
+### enableLiveMode
+`enableLiveMode` tells the query store to poll the Sanity Studio for changes and re-run the query passed to `createFetcherStore`. It takes a `client` but its important that the following `stega` information is part of the client's config.
+```javascript
+queryStore.enableLiveMode({
+    client: client.config({
+        stega: {
+            enabled: true, // enable stega encoding for visual editing to pick up on
+            studioUrl: 'http://localhost:3333', // only show overlays when inside the Studio
+        },
+    }),
+})
+```
+To allow `liveMode` to work within your Studio, you'll also need to call `enableVisualEditing` from the `@sanity/visual-editing` package
+
 
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