Smooth phrasing in under-the-hood graph update passage

[grokspawn]

Description of the change:
Attempt to make verbiage less complex by:

• removing commentary
• eliminating passive voice
• adding emphasis to distinguish between new and already-present CSV cases during graph rebuild
• eliminated paragraph references
• add whitespace to delimit complete thoughts and focus the eye on the fact that they were discrete

Motivation for the change:
As a first-touch user reading the docs, I found it difficult to follow the graph update section and thought it could be simplified while retaining intent

Reviewer Checklist

• Implementation matches the proposed design, or proposal is updated to match implementation
• Sufficient unit test coverage
• Sufficient end-to-end test coverage
• Docs updated or added to /docs
• Commit messages sensible and descriptive

[openshift-ci]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[codecov]

Codecov Report

Merging #946 (36df550) into master (aabc493) will increase coverage by 0.97%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #946      +/-   ##
==========================================
+ Coverage   52.35%   53.32%   +0.97%     
==========================================
  Files         103      103              
  Lines        9136     9449     +313     
==========================================
+ Hits         4783     5039     +256     
- Misses       3448     3476      +28     
- Partials      905      934      +29     

Impacted Files	Coverage Δ
alpha/declcfg/diff_include.go	70.21% <0.00%> (+2.28%)	⬆️
alpha/action/diff.go	79.64% <0.00%> (+2.59%)	⬆️
alpha/declcfg/diff.go	84.25% <0.00%> (+3.52%)	⬆️

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[timflannagan]

/lgtm