feat: add collapsable example section

Author: frectonz

README.md

@@ -3,3 +3,16 @@
 <img src="./logo.jpeg" alt="pg-when-logo" width="256" align="right" style="margin: 0 0 1em 1em;"/>
 
 A PostgreSQL extension for creating time values with natural language.
+
+<details>
+
+<summary>Example 1: Relative Past in a Specific Timezone</summary>
+
+```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');
+SELECT millis_at('5 days ago at this hour in Asia/Tokyo');
+SELECT micros_at('5 days ago at this hour in Asia/Tokyo');
+```
+
+</details>