move trail images documentation, rename and reformat headings slightly to fit with new docs layout

Author: jfsoul

IMAGES.md renamed to docs/06-features-and-components/02-trail-images.md

@@ -1,20 +1,18 @@
-# Images
-
-## How are trail pictures picked in Frontend?
+# How are trail pictures picked in Frontend?
 
 Use the rules below like a filter to narrow down the content api response into a list of candidate images.
 From the candidate images, choose the master 5:3 image, or simply the largest 5:3 if a master wasn't found.
 
-### Default rules
+## Default rules
 1. Use the trail pic (known in content api as 'image element with thumbnail relation'), if it contains an image with width >= 460.
 2. Use the main picture.
 3. Use the image from the first embedded video
 4. Fall back to small trail pic.
 
-### For a Gallery
+## For a Gallery
 1. Only use the thumbnail.
 
-### For a Facia card
+## For a Facia card
 1. Use the Image override if specified.
 2. If the card is a Gallery, use the Gallery behaviour.
-3. Use the default rules.
+3. Use the default rules.

docs/README.md

@@ -39,6 +39,7 @@
 
 ##[Features and components](06-features-and-components/)
 - [SteadyPage JS utility](06-features-and-components/01-steadypage-js-utility.md)
+- [How are trail pictures picked in Frontend?](06-features-and-components/02-trail-images.md)
 
 ##[Performance](07-performance/)
 - [Performance reading list](07-performance/01-performance-reading.md)