Merge pull request hashicorp#14646 from hashicorp/f-update-route-tabl…

…e-docs-note

docs/aws: add note for aws_route_table resource

website/source/docs/providers/aws/r/route_table.html.markdown

@@ -16,6 +16,12 @@ defined in-line. At this time you cannot use a Route Table with in-line routes
 in conjunction with any Route resources. Doing so will cause
 a conflict of rule settings and will overwrite rules.
 
+~> **NOTE on `gateway_id` and `nat_gateway_id`:** The AWS API is very foregiving with these two
+attributes and the `aws_route_table` resource can be created with a NAT ID specified as a Gateway ID attribute.
+This _will_ lead to a permanent diff between your configuration and statefile, as the API returns the correct
+parameters in the returned route table. If you're experiencing constant diffs in your `aws_route_table` resources,
+the first thing to check is whether or not you're specifying a NAT ID instead of a Gateway ID, or vice-versa.
+
 ## Example usage with tags:
 
 ```hcl
@@ -76,4 +82,4 @@ Route Tables can be imported using the `route table id`, e.g.
 
 ```
 $ terraform import aws_route_table.public_rt rtb-22574640
-```
+```