[Doc] How to invoke hook for testing

[1oglop1]

During the slack discussion it came up that this is a good way of testing hooks before they are invoked.
Simply invoke hook as a script. For further testing it might be better to implement it with pytest.

if __name__ == "__main__":
    from sceptre.environment import Environment

    SCEPTRE_DIR = os.path.join(os.getcwd(), '..')
    env = Environment(SCEPTRE_DIR, "cr-lab")
    stack = env.stacks["ex_python"]
    hook = S3PackageCICD(
        environment_config=stack.environment_config,
        stack_config=stack.config,
        connection_manager=stack.connection_manager)
    r = hook.run()

[jakubincloud]

Updated the code

from sceptre.environment import Environment
    # change current directory
    os.chdir('..')
    SCEPTRE_DIR = os.path.join(os.getcwd())
    env = Environment(SCEPTRE_DIR, "cr-lab")
    print(env)
    stack = env.stacks["ex_python"]
    print(stack)
    hook = S3PackageCICD(argument='functions/ex_python', environment_config=stack.environment_config, stack_config=stack.config, connection_manager=stack.connection_manager)
    r = hook.run()

[ngfgrant]

@1oglop1 can you add/update the docs with this?

[1oglop1]

shall we include it after #389?