update question card to link to help diagram in docs (xarray-contrib#274)

* update question card to link to help diagram in docs

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Scott Henderson <[email protected]>

Author: 3 people

intro.md

@@ -26,11 +26,11 @@ Live walk-throughs of this material and more on Xarray's YouTube Channel
 ```
 
 ```{grid-item-card}
-:link: https://github.com/pydata/xarray/discussions
+:link: https://docs.xarray.dev/en/latest/help-diagram.html
 :class-header: bg-light
 Get involved 🙋
 ^^^
-Ask questions on the Xarray Discussion Forum
+Ask questions and participate in the Xarray community!
 ```
 
 ````