Cp-docker-images: Please add KAFKAREST_HEAP_OPTS to documentation

[jmarcos-cano]

I did not find any reference for KAFKAREST_HEAP_OPTS nor
KAFKAREST_JVM_PERFORMANCE_OPTS in the documentation until I went to

${COMPONENT}-run-class in here: (tail "${COMPONENT}"-start)

exec $(dirname $0)/kafka-rest-run-class io.confluent.kafkarest.KafkaRestMain "$@"

[noderat]

Yeah, so this still isn't in the documentation. Five hours later I finally found it. Wow.

[funderbar]

it is 2019 now : )

[xdsxc]

Its almost 2020 now :)

[cojamac]

It's now 2020