Docs: Mention contr. callback more prominently
Docs: Mention contr. callback more prominently

[Fixes #694]

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jnstq/paper_trail,airblade/paper_trail,airblade/paper_trail,theRealNG/paper_trail,ifeelgoods/paper_trail,devonestes/paper_trail,ifeelgoods/paper_trail,jnstq/paper_trail,theRealNG/paper_trail