Update INSTALL.md for clarity

[zackshapiro]

I made some small quality of life updates to INSTALL.md for clarity, nothing groundbreaking :)

Motivation and Context

I just want to make it easier for people to install and get started and have less questions for existing devs.

How Has This Been Tested?

I proof-read it 😄

Types of changes

Copy update

Checklist:

• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [x] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.
• [x] All new and existing tests passed.

[codecov-io]

Codecov Report

Merging #284 into master will decrease coverage by 0.11%. The diff coverage is n/a.

@@            Coverage Diff            @@
##           master    #284      +/-   ##
=========================================
- Coverage    7.53%   7.41%   -0.12%     
=========================================
  Files         219     219              
  Lines        8694    8694              
=========================================
- Hits          655     645      -10     
- Misses       8039    8049      +10

Impacted Files	Coverage Δ
...htning/Services/Misc/BlockChainHeightUpdater.swift	60.41% <0%> (-20.84%)	:arrow_down:

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