Update Readme to include VPC breaking v9.0.0 change (#637)

* Update Readme to include the breaking v9.0.0 change

Updating the readme to indicated that the high_availability flag has been deprecated after v9.0.0 and include fixes on how to resolve the issue.

* Updating main.tf and README.md

* Formatting

Author: sylviamclaughlin

vpc/README.md

@@ -18,8 +18,19 @@ High Availability mode deploys in each AZ in a region. This is what you should c
 **Please Note:** This should not be used in a PBMM Production environment.
 
 Single Zone mode deployes in the first AZ in a region that is found by the availability lookup. This will work for if you want to save money in dev.
+
 ![Diagram of the Single Zone architecture](./docs/single\_zone.png)
 
+### Breaking change with v9.0.0
+If you upgrade to v9.0.0 or above from a lower version, the `high_availability` flag is deprecated and no longer available. You will need to do the following in order to upgrade to a higher version:
+1. Remove the `high_availability` flag
+2. Instead add the following to your code:
+ ```
+   availability_zones = 3
+   cidrsubnet_newbits = 8
+```
+3. Run terraform/terragrunt plan. You should have no changes in your infrastucture.
+
 ## Requirements
 
 | Name | Version |

vpc/main.tf

@@ -19,8 +19,20 @@
 * **Please Note:** This should not be used in a PBMM Production environment.
 *
 * Single Zone mode deployes in the first AZ in a region that is found by the availability lookup. This will work for if you want to save money in dev.
+*
 * ![Diagram of the Single Zone architecture](./docs/single_zone.png)
 * 
+* 
+* ### Breaking change with v9.0.0
+* If you upgrade to v9.0.0 or above from a lower version, the `high_availability` flag is deprecated and no longer available. You will need to do the following in order to upgrade to a higher version: 
+* 1. Remove the `high_availability` flag 
+* 2. Instead add the following to your code:
+*  ```
+*    availability_zones = 3
+*    cidrsubnet_newbits = 8
+* ```
+* 3. Run terraform/terragrunt plan. You should have no changes in your infrastucture.
+*
 */
 
 resource "aws_vpc" "main" {