Add instructions on how to build the container image

[kinueng]

The README.md needs instructions on how to build the container image from Dockerfile

[thasnim-fluxone]

I have added instruction on how to build the container image from Dockerfile. Can someone please review the PR

[mbroz2]

Why are the instructions using --platform to force building for linux/amd64?

Also, the instructions use <TAG> but do not explain what this is to the user..... why not just use the default latest?

Also, the instructions don't state that they have to build the actual application first.

[thasnim-fluxone]

Why are the instructions using --platform to force building for linux/amd64?

Also, the instructions use <TAG> but do not explain what this is to the user..... why not just use the default latest?

Also, the instructions don't state that they have to build the actual application first.

Updated the instructions in README based on the review comments. Opened this PR.