Add some information to Packaging cmake wiki

[Richard Shaw]

I don't have access to edit this[1] so I hope someone who does will.

I've noticed with several packages lately that frequently the wrong
build flags are used or appened to the ones the cmake macro sets.
Sometimes this can happen because the main cmake configuration file
forces the type to "Release" (bad!) but not always.

I've found that adding: "-DCMAKE_RELEASE_TYPE=RelWithDebinfo" often
takes care of this.

Thanks,
Richard

[1] https://fedoraproject.org/wiki/Packaging:Cmake