kogito-examples README typo and payload fix

dmn-pmml-springboot-example and pmml-springboot-example

READEME.md has a wrong command:

java -jar ./target/dmn-springboot-example.jar

pmml-*-example

README.md has example response payloads but now it's more concise (the full payload is returned by http://localhost:8080/LinReg/descriptive )