Some more grammar adjustments to joins vignette

[MichaelChirico]

I particularly want to avoid using nomatch=0 which we eventually should remove.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.69%. Comparing base (e18779a) to head (56ecc74).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7086   +/-   ##
=======================================
  Coverage   98.69%   98.69%           
=======================================
  Files          79       79           
  Lines       14677    14677           
=======================================
  Hits        14486    14486           
  Misses        191      191           

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