Document spring.jmx.enabled=true

[micheljung]

spring.jmx.enabled=true needs to be set since Spring Boot 2.2, otherwise the Spring Boot Plugin won't be available.

I found that it's set here:

hawtio/examples/springboot/src/main/resources/application.properties

Line 6 in 4fcf1fa

spring.jmx.enabled=true

But I couldn't find this mentioned anywhere in the documentation (e.g. in the readme or the docs) but I think it's quite important.

I'd create a PR but I can't from the office :-(

[tadayosi]

Contributions are welcome! ;-)