[Docs] Improve the docs / Readme on the JWT Manipulator.

[leecalcote]

Current State:
Configuration and use of filter are under-described.

Desired State:
Update Readme with instructions for use.

Include an example use case.

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Contributor Resources

• Meshery documentation site
• Meshery documentation source
• Instructions for contributing to documentation

[Aisuko]

@leecalcote May I take this one? And I will show the skill of Rust.

[leecalcote]

@Aisuko I missed your comment, yes, that would be great.

@Aisuko, @felixfaisal, this ties into the efforts to provide descriptions in the service mesh catalog here - https://meshery.io/catalog. Descriptions are needed here.

[Vaibhav2154]

@leecalcote I would like take up this issue and work on it. Please assign me this