Fix debugTable creation in iframe mode

[martialblog]

See #43

[mdicss]

Thanks.
Could you add the url-parameter 'grafanaDebug' to the readme.md or somewhere to the documentation and correct the name of the parameter in the changelog.md where you have 'debugGrafana' instead of 'grafanaDebug'

[martialblog]

Thanks for the hint. I updated the changelog and added another sentence in the docs/