blueql [ddl]: Add section on TRUNCATE MODEL

Author: ohsayan

docs/blueql/2.ddl.md

@@ -271,3 +271,22 @@ DROP MODEL [IF EXISTS] [ALLOW NOT EMPTY] <space_name>.<model_name>
 DROP MODEL myspace.mymodel
 DROP ALLOW NOT EMPTY myspace.mymodel
 ```
+
+### TRUNCATE MODEL
+
+```sql
+TRUNCATE MODEL <space_name>.<model_name>
+```
+
+- **Access control**: `root` only
+- **Operational notes**:
+  - Blocking
+  - Blocks all DML queries until completion of execution
+- **Returns**:
+  - empty or error
+
+#### Examples
+
+```sql
+TRUNCATE MODEL myspace.mymodel
+```