Fix and simplify documented example compiler output

[japborst]

Full output when running in an example project below (with <showWarnings>true</showWarnings>)

As one is an INFO message and the other a COMPILATION WARNING I've cleaned the result up.

[INFO] /Users/japborst/Documents/dev/error-prone-demo/src/main/java/com/example/Example.java:[9,34] [Refaster Rule] BigDecimalRules.BigDecimalZero: Refactoring opportunity
    (see https://error-prone.picnic.tech/refasterrules/BigDecimalRules#BigDecimalZero)
  Did you mean 'return BigDecimal.ZERO;'?
[INFO] -------------------------------------------------------------
[WARNING] COMPILATION WARNING :
[INFO] -------------------------------------------------------------
[WARNING] /Users/japborst/Documents/dev/error-prone-demo/src/main/java/com/example/Example.java:[14,35] [IdentityConversion] This method invocation appears redundant; remove it or suppress this warning and add a comment explaining its purpose
    (see https://error-prone.picnic.tech/bugpatterns/IdentityConversion)
  Did you mean 'return set;' or '@SuppressWarnings("IdentityConversion") public ImmutableSet<Integer> getSet() {'?
[INFO] 1 warning
[INFO] -------------------------------------------------------------
[INFO] -------------------------------------------------------------
[ERROR] COMPILATION ERROR :
[INFO] -------------------------------------------------------------
[ERROR] warnings found and -Werror specified
[INFO] 1 error

[Stephan202]

Tnx! Suggested commit message:

Fix and simplify documented example compiler output (#297)

[rickie]

It will be cool to show this today as well, so let's roll with it!!!

[Badbond]

Looking good! Thanks! 👍