some grammatical fix and add sentence to fault tolerance

Before
---
file: build/patch/json/core/replica-set-architectures.json
source: source/core/replica-set-architectures.txt
stats:
   coleman-liau: 12.766532951289395
   flesch-ease: 37.68965590911378
   flesch-level: 11.044528728698538
   foggy:
      count: 68
      factor: 0.09742120343839542
      threshold: 3
   sentence-count: 57
   sentence-len-avg: 12
   smog-index: 9.368774924056119
   word-count: 698

After
---
file: build/patch/json/core/replica-set-architectures.json
source: source/core/replica-set-architectures.txt
stats:
   coleman-liau: 12.507042253521124
   flesch-ease: 39.031971830985924
   flesch-level: 10.856250607090825
   foggy:
      count: 66
      factor: 0.09295774647887324
      threshold: 3
   sentence-count: 58
   sentence-len-avg: 12
   smog-index: 9.223106411051027
   word-count: 710