docs(graphql-reference): clarify filtering using comma/and operator (g…

…atsbyjs#10321)

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docs/docs/graphql-reference.md

@@ -44,7 +44,13 @@ In this query `filter` and the `ne` (not equals) operator is used to show only r
 
 <iframe src="https://gatsbygraphql.sloppy.zone/?query=%7B%0A%20%20allMarkdownRemark(%0A%20%20%20%20filter%3A%20%7B%0A%20%20%20%20%20%20frontmatter%3A%20%7B%20title%3A%20%7B%20ne%3A%20%22%22%20%7D%20%7D%0A%20%20%09%7D%0A%20%20)%20%7B%0A%20%20%20%20totalCount%0A%20%20%20%20edges%20%7B%0A%20%20%20%20%20%20node%20%7B%0A%20%20%20%20%20%20%20%20frontmatter%20%7B%0A%20%20%20%20%20%20%20%20%20%20title%0A%20%20%20%20%20%20%20%20%7D%0A%20%20%20%20%20%20%7D%0A%20%20%20%20%7D%0A%20%20%7D%0A%7D%0A" width="600" height="400"></iframe>
 
-Gatsby relies on [Sift](https://www.npmjs.com/package/sift) to enable MongoDB-like query syntax for object filtering. This allows Gatsby to support operators like `eq`, `ne`, `in`, `regex` and querying nested fields through the `__` connector
+Gatsby relies on [Sift](https://www.npmjs.com/package/sift) to enable MongoDB-like query syntax for object filtering. This allows Gatsby to support operators like `eq`, `ne`, `in`, `regex` and querying nested fields through the `__` connector.
+
+It is also possible to filter on multiple fields - just separate the individual filters by a comma (works as an AND):
+
+```js
+filter: { contentType: { in: ["post", "page"] }, draft: { eq: false } }
+```
 
 A good video tutorial on this is [here](https://www.youtube.com/watch?v=Lg1bom99uGM).