Added contributors file.

CONTRIBUTORS.md

+* Jeffrey Phillips Freeman (WI2ARD) - http://JeffreyFreeman.me
+* Martin Murray (KD8LVZ)
+* Paul McMillan - https://github.com/PaulMcMillan
+* Russ Innes
+* John Hogenmiller (KB3DFZ) - https://github.com/ytjohn
+* Phil Gagnon N1HHG
+* Ben Benesh - https://github.com/bbene
+* Joe Goforth
+* Rick Eason
+* Jay Nugent
+* Pete Loveall (AE5PL)
+* darksidelemm - https://github.com/darksidelemm
+* agmuino - https://github.com/agmuino