Document Zuul metrics.  Closes #2913 (#2943)
Document Zuul metrics.  Closes #2913 (#2943)


brenuart/spring-cloud-netflix,ryanjbaxter/spring-cloud-netflix,sfat/spring-cloud-netflix,ryanjbaxter/spring-cloud-netflix,joshiste/spring-cloud-netflix,sfat/spring-cloud-netflix,sfat/spring-cloud-netflix,ryanjbaxter/spring-cloud-netflix,brenuart/spring-cloud-netflix,ryanjbaxter/spring-cloud-netflix,sfat/spring-cloud-netflix,joshiste/spring-cloud-netflix,ryanjbaxter/spring-cloud-netflix,joshiste/spring-cloud-netflix,spring-cloud/spring-cloud-netflix,sfat/spring-cloud-netflix,brenuart/spring-cloud-netflix,joshiste/spring-cloud-netflix,brenuart/spring-cloud-netflix,brenuart/spring-cloud-netflix,spring-cloud/spring-cloud-netflix,joshiste/spring-cloud-netflix