Add comment to Network Class

[itdependsnetworks]

Perhaps I am misunderstanding _return_fields as I would expect the list to be larger. For example most Class's do not have comment in there.

[codecov]

Codecov Report

Merging #170 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #170   +/-   ##
=======================================
  Coverage   84.21%   84.21%           
=======================================
  Files           7        7           
  Lines        1147     1147           
  Branches      189      189           
=======================================
  Hits          966      966           
  Misses        134      134           
  Partials       47       47

Impacted Files	Coverage Δ
infoblox_client/objects.py	86.04% <ø> (ø)	⬆️

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[itdependsnetworks]

pinging @yuewko based on previous PR's

[yuewko]

LGTM