Fix some wording issues in the selector docs

[christian-bromann]

Proposed changes

Minor issue with the selector docs.

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Checklist

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• I have added proper type definitions for new commands (if appropriate)

Further comments

Reviewers: @webdriverio/project-committers

[codecov]

Codecov Report

Merging #4939 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4939      +/-   ##
==========================================
+ Coverage   99.42%   99.42%   +<.01%     
==========================================
  Files         210      210              
  Lines        5535     5607      +72     
  Branches     1211     1240      +29     
==========================================
+ Hits         5503     5575      +72     
  Misses         29       29              
  Partials        3        3

Impacted Files	Coverage Δ
packages/webdriver/src/request.js	100% <0%> (ø)	⬆️
packages/wdio-runner/src/utils.js	100% <0%> (ø)	⬆️
packages/wdio-config/src/utils.js	100% <0%> (ø)	⬆️

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[christian-bromann]

@erwinheitzman added note to Partial Link Text as well. Anything else?

[erwinheitzman]

@christian-bromann looks ready to be merged :)