Improve CONTRIBUTING.md documentation on reviewing potentially-malicious gems
Improve CONTRIBUTING.md documentation on reviewing potentially-malicious gems

Improve the documentation.
The gem review documentation originally omitted a few points
(e.g., you have to use "-r" with diff); those are now included.

Signed-off-by: David A. Wheeler <9ae72d22d8b894b865a7a496af4fab6320e6abb2@dwheeler.com>

linuxfoundation/cii-best-practices-badge,linuxfoundation/cii-best-practices-badge,yannickmoy/cii-best-practices-badge,coreinfrastructure/best-practices-badge,coreinfrastructure/best-practices-badge,linuxfoundation/cii-best-practices-badge,taylorcoursey/cii-best-practices-badge,taylorcoursey/cii-best-practices-badge,yannickmoy/cii-best-practices-badge,yannickmoy/cii-best-practices-badge,linuxfoundation/cii-best-practices-badge,taylorcoursey/cii-best-practices-badge,taylorcoursey/cii-best-practices-badge,coreinfrastructure/best-practices-badge,yannickmoy/cii-best-practices-badge,coreinfrastructure/best-practices-badge