Fix styling of Koa vs Express docs

[shime]

• split sentences
• add commas where needed
• fix various grammar errors
• replace "node.js" with "Node"
• replace "koa" with "Koa"

[codecov[bot]]

Codecov Report

Merging #1068 into master will not change coverage. The diff coverage is n/a.

@@            Coverage Diff            @@
##            master     #1068   +/-   ##
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  Coverage   100.00%   100.00%           
=========================================
  Files            4         4           
  Lines          487       487           
  Branches       136       136           
=========================================
  Hits           487       487           

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[jonathanong]

sorry, we don't merge style-only PRs. it's not worth the git diff.

can you edit this PR to only fix:

• grammatical errors (i can't tell what they are from this diff)
• koa => Koa

[niftylettuce]

Hey @shime nice to see you here 🙌 can you fix the PR per Jonathan's comments?

[shime]

@niftylettuce 👋 thanks for reminding me, just made the fixes per Jonathan's comments.