docs - Revise README.md to describe dynamodb_enabled=false approach

[westonplatter]

Describe the Feature

Based on the native S3 locking in TF >=1.10.0, I think it would be helpful to revise the setup instructions to include a description for using the dynamodb_enabled=false approach.

I'm doing this on a client project now and would be up for contributing adjustments to the README.md for this.

Expected Behavior

The README.md explains how to setup a TF backend with dynamodb_enabled=false

Use Case

These docs will help users simplify there TF setups.

Describe Ideal Solution

There are clear instructions for setting up backend without DynamoDB

Alternatives Considered

No response

Additional Context

No response