Update to docs README

[jolheiser]

Removed the build tag since Drone no longer builds it. (Or at least there are none found, I can add it back in if needed)
Updated Discord invite to use vanity URL.
Fixed some wording.
Removed Docker image since we use netlifycms now.

[techknowlogick]

can you also update link to Hugo to their home page instead of repo?

[codecov-io]

Codecov Report

Merging #6221 into master will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #6221      +/-   ##
==========================================
+ Coverage   38.86%   38.87%   +0.01%     
==========================================
  Files         354      354              
  Lines       50210    50210              
==========================================
+ Hits        19512    19518       +6     
+ Misses      27872    27865       -7     
- Partials     2826     2827       +1

Impacted Files	Coverage Δ
routers/repo/view.go	42.07% <0%> (+0.99%)	⬆️
models/unit.go	14.28% <0%> (+14.28%)	⬆️

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[jolheiser]

@techknowlogick Done