[docs] Add FAQ question on export (#4798)

## Description

Added a question on export size.

docs/docs/photos/faq/export.md

@@ -38,3 +38,11 @@ that the original is not modified. For more details, see the
 A two way sync is not currently supported. Attempting to export data to the same
 folder that is also being watched by the Ente app will result in undefined
 behaviour (e.g. duplicate files, export stalling etc).
+
+## Why is my export size larger than my backed-up size in Ente?
+
+One possible reason could be that you have files that are in multiple different
+albums. Whenever a file is backed-up to Ente in multiple albums it will still
+count only once towards the total storage in Ente. However, during export that
+file will be downloaded multiple times to the different folders corresponding to
+said albums, causing the total export size to be larger.