Tutorial.rst: Doc on ConfigGenerator

[PrajwalM2212]

This adds documentation on how to generate config files using config generator tool

Related to coala/coala#6049

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[PrajwalM2212]

@jayvdb @Makman2 @RaiVaibhav @Nosferatul @ksdme @margobra8 Can you review this PR?

[Nosferatul]

good to go, LGTM