Update supplycrates.dm

Added the Mail Supply Crate - for those rounds when the mail room actually does something. It contains a destination tagger and 2 wraps, costing 15 points to order. Found under the Operations tab.
Merge pull request #1 from UristMcStation/master

Updating Octo's UMcS
Merge pull request #75 from Octobomb/master

Adding the mail supplies crate