[aws][docs] Add AnsibleAWSModule features to AWS developer guidelines (#38978)

lib/ansible/modules/cloud/amazon/GUIDELINES.md

@@ -43,6 +43,30 @@ Few other changes are required. One possible issue that you might encounter is t
 does not inherit methods from AnsibleModule by default, but most useful methods
 are included. If you do find an issue, please raise a bug report.
 
+When porting, keep in mind that AnsibleAWSModule also will add the default ec2
+argument spec by default. In pre-port modules, you should see common arguments
+specfied with:
+
+```
+def main():
+    argument_spec = ec2_argument_spec()
+    argument_spec.update(dict(
+        state=dict(default='present', choices=['present', 'absent', 'enabled', 'disabled']),
+        name=dict(default='default'),
+        # ... and so on ...
+    ))
+    module = AnsibleModule(argument_spec=argument_spec, ...)
+
+# can be replaced with
+def main():
+    argument_spec = dict(
+        state=dict(default='present', choices=['present', 'absent', 'enabled', 'disabled']),
+        name=dict(default='default'),
+        # ... and so on ...
+    )
+    module = AnsibleAWSModule(argument_spec=argument_spec, ...)
+```
+
 ## Bug fixing
 
 Bug fixes to code that relies on boto will still be accepted. When possible, the code should be
@@ -350,6 +374,32 @@ def describe_some_resource(client, module):
         module.fail_json_aws(e, msg="Could not describe resource %s" % name)
 ```
 
+To make use of AWSRetry easier, it can now be wrapped around a client returned
+by `AnsibleAWSModule`. any call from a client. To add retries to a client,
+create a client:
+
+```
+module.client('ec2', retry_decorator=AWSRetry.jittered_backoff(retries=10))
+```
+
+Any calls from that client can be made to use the decorator passed at call-time
+using the `aws_retry` argument. By default, no retries are used.
+
+```
+ec2 = module.client('ec2', retry_decorator=AWSRetry.jittered_backoff(retries=10))
+ec2.describe_instances(InstanceIds=['i-123456789'], aws_retry=True)
+
+# equivalent with normal AWSRetry
+@AWSRetry.jittered_backoff(retries=10)
+def describe_instances(client, **kwargs):
+    return ec2.describe_instances(**kwargs)
+
+describe_instances(module.client('ec2'), InstanceIds=['i-123456789'])
+```
+
+The call will be retried the specified number of times, so the calling functions
+don't need to be wrapped in the backoff decorator.
+
 ### Returning Values
 
 When you make a call using boto3, you will probably get back some useful information that you