Improve the documentation of imageConfig and the image resource

- Added information about the expected argument type when calling
imageResource.
- Added a warning regarding calling imageConfig with incorrect arguments.
- Added information about two properties the `image` resource provides.

Co-authored-by: jmooring

content/en/content-management/image-processing/index.md

@@ -28,7 +28,11 @@ content/
         └── sunset.jpg    <-- page resource
 ```
 
-To access an image as a page resource:
+## The Image Resource
+
+The `image` resource gives you access to image-specific attributes like the picture's `Width` and `Height`, as well as powerful processing methods and filters. More on that below.
+
+Note that the `image` resource can also be retrieved from a [global resource]({{< relref "/hugo-pipes/introduction#from-file-to-resource" >}})
 
 ```go-html-template
 {{ $image := .Resources.GetMatch "sunset.jpg" }}

content/en/functions/images/index.md

@@ -218,6 +218,8 @@ Also see the [Filter Method](/content-management/image-processing/#filter).
 
 Parses the image and returns the height, width, and color model.
 
+The `imageConfig` function takes a single parameter, a file path (_string_) relative to the _project's root directory_, with or without a leading slash.
+
 {{% funcsig %}}
 images.ImageConfig PATH
 {{% /funcsig %}}