Update documentation

[kevinwcyu]

• CONTRIBUTING: yarn watch doesn’t exist though it instructs you to use that command
• CONTRIBUTING: Suggests running go get -u github.com/grafana/grafana-plugin-sdk-go to build the backend for some reason? Is this required or outdated information?
• CONTRIBUTING: Should add the release and go workspace info
• README: Explore link and second Node graph panel link in https://github.com/grafana/x-ray-datasource#service-map do not go anywhere
• README: Alerting link in https://github.com/grafana/x-ray-datasource#alerting also doesn’t go anywhere
• README: Provision Grafana link in https://github.com/grafana/x-ray-datasource#configure-the-data-source-with-provisioning also broken
• Cross-Account Observability: Getting started cryptically says “add two API actions to the IAM policy” and the link that probably used to go to the actions is broken. Also the configuration link in the comment block is not written correctly and isn’t rendering.
• README: Pricing section is a quote block for some reason