Proof readme files are out of date

[markrtuttle]

The proof readme files copied into cbmc/proofs and cbmc/proofs/PROOFDIR are giving old instructions for how to install cbmc and run the proofs.

[archigup]

Would be good to have the installation instructions there or in the repo readme.

As a developer running the instructions in the readme (https://github.com/awslabs/aws-templates-for-cbmc-proofs/blob/master/README.md), I get to the end of the "Starting a new proof" section and make fails as I don't have cbmc installed. I then look at the readme in the proof directory which just instructs to add cbmc to your path (See https://github.com/aws/Device-Defender-for-AWS-IoT-embedded-sdk/blob/main/test/cbmc/proofs/Defender_MatchTopic/README.md).

Edit: I see there is a short blurb at the top of the repo readme but its easy to skip over it as its at the end of the intro section; a seperate section for it would make it clearer.

[markrtuttle]

Let us update all of the README files to point to the new training material.

[feliperodri]

Related to https://github.com/model-checking/cbmc-starter-kit/issues/25