Improve README for the Spring Boot sample
Improve README for the Spring Boot sample

Include details about configuring alternative context paths and provide
sample URLs.

Signed-off-by: Gregor Zurowski <5fdc67d2166bcdd1d3aa4ed45ea5a25e9b21bc20@zurowski.org>

skarsaune/hawtio,hawtio/hawtio,hawtio/hawtio,skarsaune/hawtio,skarsaune/hawtio,hawtio/hawtio,skarsaune/hawtio,hawtio/hawtio,hawtio/hawtio,skarsaune/hawtio