cmd/atlascmd: extend atlas migrate validate documentation (#784)

Author: masseelch

cmd/atlascmd/migrate.go

@@ -103,11 +103,13 @@ This command should be used whenever a manual change in the migration directory
 	// MigrateValidateCmd represents the migrate validate command.
 	MigrateValidateCmd = &cobra.Command{
 		Use:   "validate",
-		Short: "Validates the migration directories checksum.",
+		Short: "Validates the migration directories checksum and SQL statements.",
 		Long: `'atlas migrate validate' computes the integrity hash sum of the migration directory and compares it to 
-the atlas.sum file. If there is a mismatch it will be reported.`,
+the atlas.sum file. If there is a mismatch it will be reported. If the --dev-url flag is given, the migration files are 
+executed on the connected database in order to validate SQL semantics.`,
 		Example: `  atlas migrate validate
-  atlas migrate validate --dir /path/to/migration/directory`,
+  atlas migrate validate --dir /path/to/migration/directory
+  atlas migrate validate --dir /path/to/migration/directory --dev-url mysql://user:pass@localhost:3306/dev`,
 		RunE: CmdMigrateValidateRun,
 	}
 )

doc/md/cli/reference.md

@@ -136,7 +136,7 @@ atlas migrate new
 
 ### atlas migrate validate
 
-Validates the migration directories checksum.
+Validates the migration directories checksum and SQL statements.
 
 #### Usage
 ```
@@ -145,13 +145,15 @@ atlas migrate validate [flags]
 
 #### Details
 'atlas migrate validate' computes the integrity hash sum of the migration directory and compares it to 
-the atlas.sum file. If there is a mismatch it will be reported.
+the atlas.sum file. If there is a mismatch it will be reported. If the --dev-url flag is given, the migration files are 
+executed on the connected database in order to validate SQL semantics.
 
 #### Example
 
 ```
   atlas migrate validate
   atlas migrate validate --dir /path/to/migration/directory
+  atlas migrate validate --dir /path/to/migration/directory --dev-url mysql://user:pass@localhost:3306/dev
 ```
 #### Flags
 ```