readability: rs-hidden-members + move some content to tuturial

Old
---
file: build/rs-hidden/json/core/replica-set-hidden-member.json
source: source/core/replica-set-hidden-member.txt
stats:
   coleman-liau: 12.233739130434781
   flesch-ease: 36.2294816053512
   flesch-level: 12.60130434782609
   foggy:
      count: 19
      factor: 0.08260869565217391
      threshold: 3
   sentence-count: 13
   sentence-len-avg: 17
   smog-index: 10.035473477838034
   word-count: 230
New
---
file: build/rs-hidden/json/core/replica-set-hidden-member.json
source: source/core/replica-set-hidden-member.txt
stats:
   coleman-liau: 11.444660194174755
   flesch-ease: 42.586928802589
   flesch-level: 10.731048543689322
   foggy:
      count: 14
      factor: 0.06796116504854369
      threshold: 3
   sentence-count: 15
   sentence-len-avg: 13
   smog-index: 8.648137234880735
   word-count: 206