Update available commands for tbls

[omuomugin]

As I was reading README.md, I realized that message which printed by tbls help doc was old and missing some command flags so just adding those for future readers.

However thanks for the fantastic tool.
This is saving our project so just keep up the great work.

[codecov]

Codecov Report

Merging #329 (33d90a9) into main (588b90f) will decrease coverage by 0.06%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #329      +/-   ##
==========================================
- Coverage   66.73%   66.66%   -0.07%     
==========================================
  Files          26       26              
  Lines        4350     4350              
==========================================
- Hits         2903     2900       -3     
- Misses       1157     1159       +2     
- Partials      290      291       +1     

Impacted Files	Coverage Δ
datasource/datasource.go	40.14% <0.00%> (-2.12%)	⬇️

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[k1LoW]

Thank you!