feat: add collapsable example section description

Author: frectonz

README.md

@@ -8,6 +8,8 @@ A PostgreSQL extension for creating time values with natural language.
 
 <summary>Example 1: Relative Past in a Specific Timezone</summary>
 
+Gets the timestamp for the beginning of the current hour, but 5 days ago, in the `Asia/Tokyo` timezone.
+
 ```sql
 SELECT when_is('5 days ago at this hour in Asia/Tokyo');
 SELECT seconds_at('5 days ago at this hour in Asia/Tokyo');