docs: Add training doc

[alexec]

[codecov]

Codecov Report

Merging #5777 (17a13e6) into master (cb55cba) will decrease coverage by 0.01%.
The diff coverage is n/a.

❗ Current head 17a13e6 differs from pull request most recent head 4176cd3. Consider uploading reports for the commit 4176cd3 to get more accurate results

@@            Coverage Diff             @@
##           master    #5777      +/-   ##
==========================================
- Coverage   46.93%   46.91%   -0.02%     
==========================================
  Files         244      244              
  Lines       15313    15313              
==========================================
- Hits         7187     7184       -3     
- Misses       7219     7220       +1     
- Partials      907      909       +2     

Impacted Files	Coverage Δ
workflow/metrics/server.go	12.50% <0.00%> (-4.17%)	⬇️
workflow/controller/operator.go	70.85% <0.00%> (-0.27%)	⬇️
cmd/argo/commands/get.go	56.95% <0.00%> (+0.64%)	⬆️
cmd/argoexec/commands/emissary.go	50.00% <0.00%> (+1.56%)	⬆️

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[terrytangyuan]

Looks great! Are you planning to migrate the course assets to this repo too?

[dinever]

Looks great! Just pointing out some typos

[alexec]

Looks great! Are you planning to migrate the course assets to this repo too?

No. Changing this repo requires PRs and each needs a detailed review. I want to avoid that for Katacoda lessons.