Add CLEAR SPACE in cheatsheet (#1384)

docs-2.0/2.quick-start/6.cheatsheet-for-ngql.md

@@ -384,6 +384,7 @@
 | [USE](../3.ngql-guide/9.space-statements/2.use-space.md) | `USE <graph_space_name>`                                     | `USE space1`                                          | Specifies a graph space as the current working graph space for subsequent queries. |
 | [SHOW SPACES](../3.ngql-guide/9.space-statements/3.show-spaces.md) | `SHOW SPACES`                                                | `SHOW SPACES`                                         | Lists all the graph spaces in the Nebula Graph examples.                         |
 | [DESCRIBE SPACE](../3.ngql-guide/9.space-statements/4.describe-space.md) | `DESC[RIBE] SPACE <graph_space_name>`                        | `DESCRIBE SPACE basketballplayer`                     | Returns the information about the specified graph space.息。                                       |
+| [CLEAR SPACE](../3.ngql-guide/9.space-statements/6.clear-space.md) | `CLEAR SPACE [IF EXISTS] <graph_space_name>` | Deletes the vertices and edges in a graph space, but does not delete the graph space itself and the schema information. |
 | [DROP SPACE](../3.ngql-guide/9.space-statements/5.drop-space.md) | `DROP SPACE [IF EXISTS] <graph_space_name>`                  | `DROP SPACE basketballplayer`                         | Deletes everything in the specified graph space.                                   |
 
 ## TAG statements