Added documentation for the intertx module

[croyyds]

[croyyds]

Before submitting the controller chain submission transaction, some minor modification is required on the tx.json generated with the --generate-only flag. In comparison, the tx.json generated for the authz module through the --generate-only flag can be directly executed for an authz exec transaction. May consider modifying the CLI on the intertx module to line this up with the authz module so that such modification on tx.json is not necessary for better user experience.

[croyyds]

The connection ID should probably be abstracted (to something like host chain ID) for better user experience.