[docs] Corrections to nodeos storage and read modes

[gleehokie]

Change Description

• Fix incorrect period placement
• Change housekeep -> track
• Spelling correction
• Nodeos no longer "keeps the database in memory", sentence changed to be correct
• Other highlighting and minor corrections

I stopped reviewing at the "Nodeos RPC API" section.

Change Type

Select ONE:

• Documentation

• Stability bug fix

• Other

• Other - special case

Testing Changes

Select ANY that apply:

• New Tests

• Existing Tests

• Test Framework

• CI System

• Other

Consensus Changes

• Consensus Changes

API Changes

• API Changes

Documentation Additions

• Documentation Additions