Updated minikube installation guide

[rscampos]

A problem was found when 'docker' driver is used with minikube.
Just ensure 'virtualbox' driver is set.

[codecov-commenter]

Codecov Report

Merging #471 (2bfb49c) into master (2ce9130) will increase coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #471      +/-   ##
==========================================
+ Coverage   37.99%   38.05%   +0.05%     
==========================================
  Files          21       21              
  Lines        8977     8977              
==========================================
+ Hits         3411     3416       +5     
+ Misses       5173     5163      -10     
- Partials      393      398       +5     

Impacted Files	Coverage Δ
KubeArmor/feeder/policyMatcher.go	39.23% <0.00%> (+0.23%)	⬆️
KubeArmor/common/common.go	48.33% <0.00%> (+1.66%)	⬆️

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