cosmetic changes to the NLB documentation

[kishorj]

Use relative references for subnets discovery page
Fix mkdocs rendering of prerequisites section

[codecov-commenter]

Codecov Report

Merging #2010 (52208cf) into main (68c417a) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #2010   +/-   ##
=======================================
  Coverage   49.24%   49.24%           
=======================================
  Files         130      130           
  Lines        7034     7034           
=======================================
  Hits         3464     3464           
  Misses       3292     3292           
  Partials      278      278           

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[M00nF1sh]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: kishorj, M00nF1sh

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