document DMD style more prominently

[thewilsonator]

#9511 minus the controversial items.

[dlang-bot]

Thanks for your pull request and interest in making D better, @thewilsonator! We are looking forward to reviewing it, and you should be hearing from a maintainer soon.
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Testing this PR locally

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[jacob-carlborg]

Half of the tests don't pass 😢.

[thewilsonator]

DAutoTest has a network problem, circle fails regularly for network and environmental reasons, semaphore fails because bootstrap with GDC8 got broken recently.