[DOC] Add testing workflow guidance for sktime-mcp

[Adithyaphani]

Reference Issues/PRs

Addresses #35

What does this implement/fix? Explain your changes.

This PR adds focused documentation for testing sktime-mcp workflows, aligned
with the feedback requested in issue #35.

The added section explains how contributors can test:

• running the MCP server
• estimator discovery and description
• forecasting workflows with demo datasets
• custom data loading
• async fit/predict workflows
• structured feedback reporting

This is intended to make it easier for new contributors and early adopters to
test the project consistently and provide useful feedback.

What should a reviewer concentrate their feedback on?

• Whether the testing workflow guidance is accurate
• Whether the listed workflows match the current MCP tools
• Whether the feedback template is useful for contributors

Did you add any tests for the change?

No. This is a documentation-only change.

Any other comments?

This PR is intentionally scoped to documentation improvements requested by the
testing/feedback issue.

[Adithyaphani]

@Shashankss1205 I think changes can be clearly merged . Looking forward to your reply on this.