Update collector.process.md

Documented IIS worker process apppool matching.

Discovered this feature at [process.go:221](https://github.com/prometheus-community/windows_exporter/blob/eb73859393991318a6ae08da53f863cee4a9d2a1/collector/process.go#L221). This also solves issue #1074.

Signed-off-by: MarNicGit <[email protected]>

docs/collector.process.md

@@ -1,6 +1,6 @@
-# process collector
+# Process collector
 
-The process collector exposes metrics about processes
+The process collector exposes metrics about processes.
 
 |||
 -|-
@@ -37,6 +37,21 @@ To specify multiple names, use the pipe `|` character:
 ```
 This will match all processes named `firefox`, `FIREFOX` or `chrome` .
 
+## IIS Worker processes
+
+The process collector also queries the `root\\WebAdministration` WMI namespace to check for running IIS workers. If it succesfully retrieves a list from this namespace, it will append the name of the worker's application pool to the corresponding process. Whitelist/blacklist matching occurs before this name is appended, so you don't have to take this name in consideration when writing your expression.
+
+Note that this specific feature **only works** if the [IIS Management Scripts and Tools](https://learn.microsoft.com/en-us/iis/manage/scripting/managing-sites-with-the-iis-wmi-provider) are installed. If they are not installed then all worker processes return as just `w3wp`.
+
+### Example
+
+Given an IIS server with two websites called "Prometheus.io" and "Example.com" running under the application pools "Public website" and "Test", the process names returned will look as follows:
+
+```
+w3wp_Public website
+w3wp_Test
+```
+
 ## Metrics
 
 Name | Description | Type | Labels