Create a Docker image for contributor use

[omerbensaadon]

Description:

We have added a number of extensions to the existing Material for MkDocs deployment and need to create a Docker image which reflects those additions.

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Story

As Carlos the Contributor 
I want to leverage a Docker image to work on the docs/website
So that I don't have to deal with local tooling 
And I can contribute to docs in the way that is most comfortable for me 

Acceptance Criteria

Docker Image Works

GIVEN a Docker image has been created for Knative's deployment of MkDocs 
WHEN I follow the instructions on https://hub.docker.com/r/squidfunk/mkdocs-material/, substituting the link to the new Docker image
THEN I can successfully render the Knative site without errors on my local machine 

Documentation Exists

GIVEN I want to use the Docker image for a local deployment of the Knative.dev website 
WHEN I look follow the link https://dev-knative.netlify.app/development/getting-started/contributing/contributing/#use-the-docker-container
THEN I see some basic instructions for getting the Docker Image to work. 

Known Issues and Considerations:

See https://dev-knative.netlify.app/development/getting-started/contributing/contributing/#install-knative-specific-extensions for a list of the extensions we currently use. They are reproduced below:

mkdocs-material-extensions 
mkdocs-macros-plugin 
mkdocs-exclude 
mkdocs-awesome-pages-plugin 
mkdocs-redirects

You may also want to check the mkdocs.yaml file for any we've missed?

Who should probably pick up this issue?

• Existing Contributors
• New Contributors