Document that Lambda service is regional

[trivikr]

Is your feature request related to a problem? Please describe.

User may not be aware that Lambda is regional, and they'll need to run scripts after setting different regions.

Describe the solution you'd like

• Provide instructions on how to find out which region has most Lambda functions, and set it while running the CLI.
• Accept --region as an option to run command on.

We can also explicitly ask for region, and also allow user to select all regions

Additional context

Refs: #1 (comment)

[kuhe]

aws account list-regions

the list regions operation may be useful