Add-collect()-examples (#2321)

docs-2.0/3.ngql-guide/6.functions-and-expressions/15.aggregating.md

@@ -260,6 +260,31 @@ nebula> MATCH (n:player) \
 | 25  | ["Joel Embiid", "Kyle Anderson"]                                         |
 +-----+--------------------------------------------------------------------------+
 ...
+
+nebula> GO FROM "player100" OVER serve \
+        YIELD properties($$).name AS name \
+        | GROUP BY $-.name \
+        YIELD collect($-.name) AS name;
++-----------+
+| name      |
++-----------+
+| ["Spurs"] |
++-----------+
+
+nebula> LOOKUP ON player \
+        YIELD player.age As playerage \
+        | GROUP BY $-.playerage \
+        YIELD collect($-.playerage) AS playerage;
++------------------+
+| playerage        |
++------------------+
+| [22]             |
+| [47]             |
+| [43]             |
+| [25, 25]         |
++------------------+
+...
+
 ```
 
 ## 聚合示例