docs(README): add note on Bad Request

Author: notrab

demo/graphcms-fragments/Product.graphql

@@ -38,11 +38,26 @@ fragment Product on Product {
   }
   price
   test {
-    ... on RichText {
+    ... on ProductTestRichText {
       raw
+      json
       html
       markdown
       text
+      references {
+        ... on Asset {
+          remoteTypeName: __typename
+          remoteId: id
+          locale
+          stage
+        }
+        ... on Category {
+          remoteTypeName: __typename
+          remoteId: id
+          locale
+          stage
+        }
+      }
     }
   }
   createdBy {

gatsby-source-graphcms/README.md

@@ -265,6 +265,8 @@ module.exports = {
 
 Enabling this option adds a `markdownNode` nested field to all `RichText` fields on the generated Gatsby schema.
 
+You will need to rebuild your `graphcms-fragments` if you enable embeds on a Rich Text field, or you add/remove additional fields to your GraphCMS schema.
+
 #### Usage with `gatsby-plugin-mdx`
 
 These newly built nodes can be used with [`gatsby-plugin-mdx`](https://www.gatsbyjs.org/packages/gatsby-plugin-mdx) to render markdown from GraphCMS.
@@ -380,3 +382,12 @@ If it's already included, make sure you have your ENV variable added to `.env`,
 This error occurs most likely if your token doesn't have access to the `PUBLISHED` content stage. Configure your token to also access `PUBLISHED`, or specify `stages: ["DRAFT"]` to the options inside `gatsby-config.js`.
 
 </details>
+
+<details>
+  <summary>Bad request</summary>
+
+You may need to rebuild your fragments folder when making schema changes. If you change the type of a field, or add/remove any from an existing model you have fragments for, the plugin cannot query for this.
+
+Simply delete the `graphcms-fragments` (or whatever you named it), and run `gatsby develop` to regenerate.
+
+</details>