message: Fixed issue with pipeline execution command in get-start document.
diff: @@ -288,13 +288,13 @@ Q1. Find the vertexes that 201 likes:
  ```
  nebula> GO FROM 201 OVER like;
  -=======
  -| id |
  -=======
  +=============
  +| like._dst |
  +=============
  | 200 |
  --------
  +-------------
  | 202 |
  --------
  +-------------
  ```
  Q2. Find the vertexes that 201 likes, whose ages are greater than 17. Return their name, age and gender, and alias the columns as Friend, Age and Gender, respectively.
  @@ -319,7 +319,7 @@ Q3. Find the selected courses and corresponding grades of students liked by 201.
  ```
  -- By pipe
  -nebula> GO FROM 201 OVER like | GO FROM $-.id OVER select YIELD $^.student.name AS Student, $$.course.name AS Course, select.grade AS Grade;
  +nebula> GO FROM 201 OVER like yield like._dst as id | GO FROM $-.id OVER select YIELD $^.student.name AS Student, $$.course.name AS Course, select.grade AS Grade;
  =============================
  | Student | Course | Grade |
  @@ -332,7 +332,7 @@ nebula> GO FROM 201 OVER like | GO FROM $-.id OVER select YIELD $^.student.name
  -----------------------------
  -- By temporary variable
  -nebula> $a=GO FROM 201 OVER like; GO FROM $a.id OVER select YIELD $^.student.name AS Student, $$.course.name AS Course, select.grade AS Grade;
  +nebula> $a=GO FROM 201 OVER like yield like._dst as id; GO FROM $a.id OVER select YIELD $^.student.name AS Student, $$.course.name AS Course, select.grade AS Grade;
  =============================
  | Student | Course | Grade |
  