improve changelog entry

Author: Etienne Laurent

.editorconfig

@@ -9,3 +9,6 @@ indent_size = 2
 indent_style = space
 insert_final_newline = true
 trim_trailing_whitespace = true
+
+[*.md]
+trim_trailing_whitespace = false

CHANGELOG.md

@@ -22,7 +22,10 @@
 * Adds possibility for modules to [add extra frontend bundles for scss and js](https://v3.docs.apostrophecms.org/guide/webpack.html). This is useful when the `ui/src` build would otherwise be very large due to code used on rarely accessed pages.
 * Loads the right bundles on the right pages depending on the page template and the loaded widgets. Logged-in users have all the bundles on every page, because they might introduce widgets at any time.
 * Fixes deprecation warnings displayed after running `npm install`, for dependencies that are directly included by this package.
-* Implement custom ETags emission. It allows caching of pages and pieces, using a cache invalidation mechanism that takes into account related (and reverse related) documents updates, thanks to backlinks mentioned above. For now, only single pages and pieces benefit from the ETags caching system (pages' and pieces' `getOne` REST API route, and regular served pages).
+* Implement custom ETags emission when `etags` cache option is enabled. [See the documentation for more information](https://v3.docs.apostrophecms.org/guide/caching.html).  
+It allows caching of pages and pieces, using a cache invalidation mechanism that takes into account related (and reverse related) document updates, thanks to backlinks mentioned above.  
+Note that for now, only single pages and pieces benefit from the ETags caching system (pages' and pieces' `getOne` REST API route, and regular served pages).  
+The cache of an index page corresponding to the type of a piece that was just saved will automatically be invalidated. However, please consider that it won't be effective when a related piece is saved, therefore the cache will automatically be invalidated _after_ the cache lifetime set in `maxAge` cache option.
 
 ### Fixes