add microbadger badge and docker tag info

.readme/about.md

 ## About
 
+API server for the Motion Bank Systems
+
+## Docker
+
+[![](https://images.microbadger.com/badges/image/motionbank/api.svg)](https://microbadger.com/images/motionbank/api "Get your own image badge on microbadger.com")
+
+The docker image can be pulled with the tag `motionbank/api:latest`.