add note on security since it has come up several times on gitter (#1982)
add note on security since it has come up several times on gitter (#1982)


twitter/zipkin,openzipkin/zipkin,openzipkin/zipkin,openzipkin/zipkin,twitter/zipkin,adriancole/zipkin,adriancole/zipkin,openzipkin/zipkin,twitter/zipkin,openzipkin/zipkin,twitter/zipkin,adriancole/zipkin,adriancole/zipkin