docs: Prepare for new sub tree

See #11925

docs/content/en/functions/images/Sigmoid.md

@@ -1,40 +0,0 @@
----
-title: images.Sigmoid
-description: Returns an image filter that changes the contrast of an image using a sigmoidal function.
-categories: []
-keywords: []
-action:
-  aliases: []
-  related:
-    - functions/images/Filter
-    - methods/resource/Filter
-  returnType: images.filter
-  signatures: [images.Sigmoid MIDPOINT FACTOR]
-toc: true
----
-
-This is a non-linear contrast change useful for photo adjustments; it preserves highlight and shadow detail.
-
-The midpoint is the midpoint of contrast. It must be in the range [0, 1], typically 0.5.
-
-The factor indicates how much to increase or decrease the contrast, typically in the range [-10, 10] where 0 has no effect. A positive value increases contrast, while a negative value decrease contrast.
-
-## Usage
-
-Create the filter:
-
-```go-html-template
-{{ $filter := images.Sigmoid 0.6 -4 }}
-```
-
-{{% include "functions/images/_common/apply-image-filter.md" %}}
-
-## Example
-
-{{< img
-  src="images/examples/zion-national-park.jpg"
-  alt="Zion National Park"
-  filter="Sigmoid"
-  filterArgs="0.6,-4"
-  example=true
->}}