Fix from_unixtime function documentation (apache#15844)

* Fix `from_unixtime` function documentation

* Update scalar_functions.md

Author: Viicos

datafusion/functions/src/datetime/from_unixtime.rs

@@ -31,7 +31,7 @@ use datafusion_macros::user_doc;
 
 #[user_doc(
     doc_section(label = "Time and Date Functions"),
-    description = "Converts an integer to RFC3339 timestamp format (`YYYY-MM-DDT00:00:00.000000000Z`). Integers and unsigned integers are interpreted as nanoseconds since the unix epoch (`1970-01-01T00:00:00Z`) return the corresponding timestamp.",
+    description = "Converts an integer to RFC3339 timestamp format (`YYYY-MM-DDT00:00:00.000000000Z`). Integers and unsigned integers are interpreted as seconds since the unix epoch (`1970-01-01T00:00:00Z`) return the corresponding timestamp.",
     syntax_example = "from_unixtime(expression[, timezone])",
     sql_example = r#"```sql
 > select from_unixtime(1599572549, 'America/New_York');

docs/source/user-guide/sql/scalar_functions.md

@@ -2133,7 +2133,7 @@ _Alias of [date_trunc](#date_trunc)._
 
 ### `from_unixtime`
 
-Converts an integer to RFC3339 timestamp format (`YYYY-MM-DDT00:00:00.000000000Z`). Integers and unsigned integers are interpreted as nanoseconds since the unix epoch (`1970-01-01T00:00:00Z`) return the corresponding timestamp.
+Converts an integer to RFC3339 timestamp format (`YYYY-MM-DDT00:00:00.000000000Z`). Integers and unsigned integers are interpreted as seconds since the unix epoch (`1970-01-01T00:00:00Z`) return the corresponding timestamp.
 
 ```sql
 from_unixtime(expression[, timezone])