Added hyperlink to Prometheus (#28196)

Hi - I have added hyperlink to Prometheus. Pls review and merge.

Thanks,
Ashish

docs/sources/explore/index.md

@@ -35,7 +35,7 @@ If you want to start with an existing query in a panel, choose the Explore optio
 
 {{< docs-imagebox img="/img/docs/v65/explore_panel_menu.png" class="docs-image--no-shadow" caption="Screenshot of the new Explore option in the panel menu" >}}
 
-Choose your data source from the dropdown in the top left. Prometheus has a custom Explore implementation, the other data sources use their standard query editor.
+Choose your data source from the dropdown in the top left. [Prometheus](https://grafana.com/oss/prometheus/) has a custom Explore implementation, the other data sources use their standard query editor.
 
 The query field is where you can write your query and explore your data. There are three buttons beside the query field, a clear button (X), an add query button (+) and the remove query button (-). Just like the normal query editor, you can add and remove multiple queries.