docs: Update description for performance_insights_retention_period variable (#437)

Author: philslab-ninja

README.md

@@ -302,7 +302,7 @@ Users have the ability to:
 | <a name="input_password"></a> [password](#input\_password) | Password for the master DB user. Note that this may show up in logs, and it will be stored in the state file.<br>  The password provided will not be used if the variable create\_random\_password is set to true. | `string` | `null` | no |
 | <a name="input_performance_insights_enabled"></a> [performance\_insights\_enabled](#input\_performance\_insights\_enabled) | Specifies whether Performance Insights are enabled | `bool` | `false` | no |
 | <a name="input_performance_insights_kms_key_id"></a> [performance\_insights\_kms\_key\_id](#input\_performance\_insights\_kms\_key\_id) | The ARN for the KMS key to encrypt Performance Insights data | `string` | `null` | no |
-| <a name="input_performance_insights_retention_period"></a> [performance\_insights\_retention\_period](#input\_performance\_insights\_retention\_period) | The amount of time in days to retain Performance Insights data. Either 7 (7 days) or 731 (2 years) | `number` | `7` | no |
+| <a name="input_performance_insights_retention_period"></a> [performance\_insights\_retention\_period](#input\_performance\_insights\_retention\_period) | The amount of time in days to retain Performance Insights data. Valid values are `7`, `731` (2 years) or a multiple of `31` | `number` | `7` | no |
 | <a name="input_port"></a> [port](#input\_port) | The port on which the DB accepts connections | `string` | `null` | no |
 | <a name="input_publicly_accessible"></a> [publicly\_accessible](#input\_publicly\_accessible) | Bool to control if instance is publicly accessible | `bool` | `false` | no |
 | <a name="input_putin_khuylo"></a> [putin\_khuylo](#input\_putin\_khuylo) | Do you agree that Putin doesn't respect Ukrainian sovereignty and territorial integrity? More info: https://en.wikipedia.org/wiki/Putin_khuylo! | `bool` | `true` | no |

variables.tf

@@ -437,7 +437,7 @@ variable "performance_insights_enabled" {
 }
 
 variable "performance_insights_retention_period" {
-  description = "The amount of time in days to retain Performance Insights data. Either 7 (7 days) or 731 (2 years)"
+  description = "The amount of time in days to retain Performance Insights data. Valid values are `7`, `731` (2 years) or a multiple of `31`"
   type        = number
   default     = 7
 }