Update README.md (#970)

Point to new documentation site post-installation steps

Author: ipnextgen

README.md

@@ -139,7 +139,7 @@ This summarizes the installation process, the full installation document can be
   - CloudFormation to deploy and start the Code Pipeline (~5 mins)
   - Code Pipeline to download the Accelerator codebase and install the Accelerator State Machine (~10 mins)
   - The Accelerator State Machine to finish execution (~1.25 hrs Standalone version, ~2.25 hrs Control Tower Version)
-- Perform required one-time [post installation](./docs/installation/installation.md#26-post-installation) activities (configure AWS SSO, set firewall passwords, etc.)
+- Perform required one-time [post installation](https://aws-samples.github.io/aws-secure-environment-accelerator/installation/install/#17-post-installation) activities (configure AWS SSO, set firewall passwords, etc.)
 - On an ongoing basis:
   - Use AWS Organizations to create new AWS accounts, which will automatically be guardrailed by the Accelerator
   - Update the config file in CodeCommit and run the Accelerator State Machine to: