feat: Azure region & stage defaults

docs/DEPLOY.md

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+# Overview
+
+Deploy usage guide and design decision.
+
+## Multi-stage, multi-region deploy
+
+By default, all functions are deploy to a stage (`dev`) and a region.  The
+autogenerated resource group name will reflect this information.  The name 
+follow the Microsoft recommended [naming convention](https://docs.microsoft.com/en-us/azure/architecture/best-practices/naming-conventions#general).
+
+### Using exitsing resource group
+
+`sls deploy -s dev -r westus2 -g myResourceGroup`
+
+- Use resource group `myResourceGroup`
+- Create/Update app service plan, app service
+- Zipdeploy code
+
+### No resource group specified
+
+`sls deploy -s dev -r westus2`
+
+- Create if not exist resource group `<service>-dev-westus2-rg`
+- Create/Update app service plan, app service
+- Zipdeploy code
+
+### Design decision on resource group support
+
+#### Specifying resourceGroup in serverless.yml
+
+- it is not clear if a resourceGroup has already been associated with a given stage and region.  
+
+For example, we have the following default config
+
+```yaml
+provider:
+  stage: dev
+  region: westus
+  resourceGroup: myResourceGroup
+```
+
+then user try to deploy
+`sls deploy -s prod -r westus`
+
+1. Do we use the environment variables / creds associated with `dev` or `prod`?
+1. Someone new to the codecase see both the `serverless.yaml` and the command in a CD script, how can they tell which resourceGroup goes where.
+
+#### Specifying resourceGroup in command line
+
+`sls deploy -s prod -r westus -g prodResourceGroup`
+
+1. With this format, it's more clear which stage+region combo is associated with a resourceGroup.  
+1. User can still make mistake, however, and use the `wrong` resource group for a specific stage.
+
+#### Don't support user defined resource group
+
+1. always using the right resource group
+1. restrictive for user who have already defined their resources