Improve doc of movingAverage (#11262)

* Make doc more directive

Signed-off-by: frank chen <frank.chen021@outlook.com>

* Add limitation

Signed-off-by: frank chen <frank.chen021@outlook.com>

* Suppress spelling check error

docs/development/extensions-contrib/moving-average-query.md

@@ -50,12 +50,28 @@ It runs the query in two main phases:
 
 
 ## Operations
-To use this extension, make sure to [load](../../development/extensions.md#loading-extensions) `druid-moving-average-query` only to the Broker.
+
+### Installation
+Use [pull-deps](../../operations/pull-deps.md) tool shipped with Druid to install this [extension](../../development/extensions.md#community-extensions) on all Druid broker nodes.
+
+```bash
+java -classpath "<your_druid_dir>/lib/*" org.apache.druid.cli.Main tools pull-deps -c org.apache.druid.extensions.contrib:druid-moving-average-query:{VERSION}
+```
+
+### Enabling
+After installation, to enable this extension, just add `druid-moving-average-query` to `druid.extensions.loadList` in brokers' `runtime.properties` file and then restart broker nodes.
+
+For example:
+
+```bash
+druid.extensions.loadList=["druid-moving-average-query"]
+```
 
 ## Configuration
 There are currently no configuration properties specific to Moving Average.
 
 ## Limitations
+* movingAverage is not supported by Druid router(including the Web Console), all queries should be sent to broker nodes directly.
 * movingAverage is missing support for the following groupBy properties: `subtotalsSpec`, `virtualColumns`.
 * movingAverage is missing support for the following timeseries properties: `descending`.
 * movingAverage is missing support for [SQL-compatible null handling](https://github.com/apache/druid/issues/4349) (So setting druid.generic.useDefaultValueForNull in configuration will give an error).

website/.spelling

@@ -584,6 +584,7 @@ longSum
 movingAverage
 postAggregations
 postAveragers
+pull-deps
  - ../docs/development/extensions-contrib/opentsdb-emitter.md
 defaultMetrics.json
 namespacePrefix