Fix a couple of issues with Heroic minimal setup

[hexedpackets]

• Fix the cache example config
• Add an entrypoint to the docker image. Right now, trying to run the command in the README for Docker will just start a bash shell

[codecov]

Codecov Report

Merging #529 into master will increase coverage by 0.01%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #529      +/-   ##
============================================
+ Coverage     49.69%   49.71%   +0.01%     
- Complexity     2899     2905       +6     
============================================
  Files           720      722       +2     
  Lines         19841    19849       +8     
  Branches       1434     1434              
============================================
+ Hits           9860     9867       +7     
- Misses         9487     9488       +1     
  Partials        494      494

Impacted Files	Coverage Δ	Complexity Δ
.../src/main/java/com/spotify/heroic/test/Points.java	100% <0%> (ø)	3% <0%> (?)
...st/src/main/java/com/spotify/heroic/test/Data.java	66.66% <0%> (ø)	2% <0%> (?)

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