Adds rationale for healthcheck config (#2812)
Adds rationale for healthcheck config (#2812)

As we routinely get FUD about slow startup or memory usage, this
documents health check parameters in efforts to avoid them being read
literally as "zipkin takes 30s to startup"

See https://github.com/openzipkin/zipkin/pull/2808
openzipkin/zipkin,openzipkin/zipkin,openzipkin/zipkin,adriancole/zipkin,twitter/zipkin,openzipkin/zipkin,openzipkin/zipkin,twitter/zipkin,adriancole/zipkin,twitter/zipkin,adriancole/zipkin,twitter/zipkin,adriancole/zipkin