docs(datasource/aws-rds): improve readme (#29870)

Co-authored-by: Rhys Arkins <rhys@arkins.net>

lib/modules/datasource/aws-rds/readme.md

 This datasource returns the database engine versions available for use on [AWS RDS](https://aws.amazon.com/rds/) via the AWS API.
+
 Generally speaking, all publicly released database versions are available for use on RDS.
 However, new versions may not be available on RDS for a few weeks or months after their release while AWS tests them.
 In addition, AWS may pull existing versions if serious problems arise during their use.
 
-**AWS API configuration**
+<!-- prettier-ignore -->
+!!! warning
+    The default versioning of the `aws-rds` datasource is _not_ compatible with [AWS Aurora](https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/CHAP_AuroraOverview.html)!
+    If you use AWS Aurora, you must set your own custom versioning.
+    Scroll down to see an example.
+
+### AWS API configuration
 
 Since the datasource uses the AWS SDK for JavaScript, you can configure it like other AWS Tools.
 You can use common AWS configuration options, for example:
@@ -14,9 +21,7 @@ You can use common AWS configuration options, for example:
 
 Read the [AWS Developer Guide - Configuring the SDK for JavaScript](https://docs.aws.amazon.com/sdk-for-javascript/v3/developer-guide/configuring-the-jssdk.html) for more information on these configuration options.
 
-The minimal IAM privileges required for this datasource are:
-
-```json
+```json title="Minimal IAM privileges needed for this datasource"
 {
   "Sid": "AllowDBEngineVersionLookup",
   "Effect": "Allow",
@@ -27,7 +32,7 @@ The minimal IAM privileges required for this datasource are:
 
 Read the [AWS RDS IAM reference](https://docs.aws.amazon.com/service-authorization/latest/reference/list_amazonrds.html) for more information.
 
-**Usage**
+### Usage
 
 Because Renovate has no manager for the AWS RDS datasource, you need to help Renovate by configuring the custom manager to identify the RDS dependencies you want updated.
 
@@ -53,16 +58,14 @@ For example:
 [{"Name":"engine","Values":["mysql"]},{"Name":"engine-version","Values":["5.7"]}]
 ```
 
-Here's an example of using the custom manager to configure this datasource:
-
-```json
+```json title="Using a custom manager to configure this datasource"
 {
   "customManagers": [
     {
       "customType": "regex",
       "fileMatch": ["\\.yaml$"],
       "matchStrings": [
-        ".*amiFilter=(?<lookupName>.+?)[ ]*\n[ ]*(?<depName>[a-zA-Z0-9-_:]*)[ ]*?:[ ]*?[\"|']?(?<currentValue>[.\\d]+)[\"|']?.*"
+        ".*rdsFilter=(?<lookupName>.+?)[ ]*\n[ ]*(?<depName>[a-zA-Z0-9-_:]*)[ ]*?:[ ]*?[\"|']?(?<currentValue>[.\\d]+)[\"|']?.*"
       ],
       "datasourceTemplate": "aws-rds"
     }
@@ -74,6 +77,33 @@ The configuration above matches every YAML file, and recognizes these lines:
 
 ```yaml
 spec:
-  # amiFilter=[{"Name":"engine","Values":["mysql"]},{"Name":"engine-version","Values":["5.7"]}]
+  # rdsFilter=[{"Name":"engine","Values":["mysql"]},{"Name":"engine-version","Values":["5.7"]}]
   engineVersion: 5.7.34
 ```
+
+#### Using Terraform, `aws-rds` datasource and Aurora MySQL
+
+Here is the Renovate configuration to use Terraform, `aws-rds` and Aurora MySQL:
+
+```json
+{
+  "customManagers": [
+    {
+      "description": "Update RDS",
+      "customType": "regex",
+      "fileMatch": [".+\\.tf$"],
+      "matchStrings": [
+        "\\s*#\\s*renovate:\\s*rdsFilter=(?<lookupName>.+?) depName=(?<depName>.*) versioning=(?<versioning>.*)\\s*.*_version\\s*=\\s*\"(?<currentValue>.*)\""
+      ],
+      "datasourceTemplate": "aws-rds"
+    }
+  ]
+}
+```
+
+The above configuration is an example of updating an AWS RDS version inside a Terraform file, using a custom manager.
+
+```
+# renovate:rdsFilter=[{"Name":"engine","Values":["aurora-mysql"]},{"Name":"engine-version","Values":["8.0"]}] depName=aurora-mysql versioning=loose
+engine_version = "8.0.mysql_aurora.3.05.2"
+```