Update graphql search doc.mdx (#989)

<!-- Explain the changes introduced in your PR -->

## Pull Request approval

You will need to get your PR approved by at least one member of the
Sourcegraph team. For reviews of docs formatting, styles, and component
usage, please tag the docs team via the #docs Slack channel.

docs/api/graphql/search.mdx

@@ -20,3 +20,7 @@ src search -json 'repo:pallets/flask error'
 ```
 
 You can then consume the JSON output directly, add `--get-curl` to get a `curl` execution line, and more. See [the `src` CLI tool](https://sourcegraph.com/github.com/sourcegraph/src-cli) for more details.
+
+## Incomplete search results when using Graphql
+
+Sometimes, users find discrepancies in the number of results returned on UI compared to Graphql for the same query. This can be avoided by adding ```"count:all" ``` to the query used in Graphql. This ensures all the matching records are being fetched via Graphql.