Add ADOPTERS.md

ADOPTERS.md

+This is an alphabetical list of our users along with year of adoption.
+Feel free to add yourself.
+
+* ARGUS
+* Boxever
+* CESANTA
+* CoreOS
+* Crononauta
+* DigitalOcean
+* docker
+* Ericsson
+* Eurotech
+* FOSDEM
+* Giant Swarm
+* Improbable
+* jodel
+* JustWatch
+* kumina
+* Latency.at
+* loodse
+* Maven Securities
+* Outbrain
+* Percona
+* Ping CAP
+* QaWare
+* QuoByte
+* RobustPerception
+* SHOWMAX
+* ShuttleCloud
+* SoundCloud
+* SpaceNet, 2015
+* Transloadit
+* uda100
+* UNO-SOFT
+* Variomedia
+* weaveworks