Add documentation on Assist in developer tools (#28132)

* Added documentation on Assist in developer tools.

* tiny tweaks

* Moved Assist section to the bottom in the same order as developer tools.

Change resulted from conflict merge resolution.

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Co-authored-by: c0ffeeca7 <38767475+c0ffeeca7@users.noreply.github.com>

source/_docs/tools/dev-tools.markdown

@@ -126,3 +126,16 @@ Another use of the {% my developer_statistics title="statistics developer tool"
 icon. Use date & time to search for the incorrect data point and adjust the value.
 
 ![Screenshot showing adjusting the long-term statistic history value](/images/blog/2022-04/adjust-statistics.png)
+
+## Assist
+
+The **Assist** tab lets you see how Home Assistant's Assist processes a sentence.
+
+If no matching intent is found, then Assist is unable to interpret the sentence. If a matching intent was found, information is provided on the action that will be performed on which entities. The example below shows how the following sentence was parsed: *what lights are on in the office*. 
+- Assist found a matching intent: *HassGetState*.
+- It found entities matching the domain: *lights*.
+- The lights have the state *on*.
+- The lights are in the area *office*. 
+- The targets are the narrowed-down entities in scope.
+
+![Example use of assist developer tools](/images/docs/developer-tools/Assist.png)