Fix document issues

[clairewu0218]

Pull Request Template

Description

Small changes to README and test plan template

Checklist

• [X] I have made corresponding changes to the documentation
• [X] I have performed a self-review of my own code

[github-actions[bot]]

Package	Line Rate	Branch Rate	Complexity	Health
Microsoft.PowerApps.TestEngine	94%	91%	826	✔
Summary	94% (2196 / 2326)	91% (524 / 576)	826	✔

Minimum allowed line rate is 50%