docs: add more clear and description comments

[jaybxyz]

Description

closes: #152

Tasks

• scan through client folder to improve comments @kogisin
• scan through keeper folder to improve comments @hallazzang
• scan through simulation folder to improve comments @kogisin (found some comments for TODOs and this is better to be handled with test: Improve public plan proposal simulations #108
• scan through types folder to improve comments @hallazzang

---

Before we can merge this PR, please make sure that all the following items have been
checked off. If any of the checklist items are not applicable, please leave them but
write a little note why.

• Appropriate labels applied
• Targeted PR against correct branch
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the module structure standards.
• Wrote unit and integration
• Updated relevant documentation (docs/) or specification (x/<module>/spec/)
• Added relevant godoc comments.
• Re-reviewed Files changed in the Github PR explorer
• Review Codecov Report in the comment section below once CI passes

[jaybxyz]

Should we R4R @hallazzang ? I'll actually go review the changes and see if there is any typo or places that need more description.

[jaybxyz]

The below line is just a minor stuff that I found. We can R4R now and change the minor stuff later when we need.

Should we remove the line?
https://github.com/kogisin/farming/blob/5ffc807b415d623dca28f59bdca9a4cf5bc57a23/x/farming/keeper/reward.go#L421

[hallazzang]

@kogisin Yes we can remove that line and make this PR ready for review.

[dongsam]

LGTM