Adding a design proposal template and README.

[tejal29]

This PR is to add design proposal template.

This template can help the core team to get a better understanding of the new feature or any big changes.
Also can serve as a guideline to follow when reviewing big changes.

[codecov-io]

Codecov Report

Merging #1838 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1838   +/-   ##
=======================================
  Coverage   47.98%   47.98%           
=======================================
  Files         143      143           
  Lines        6483     6483           
=======================================
  Hits         3111     3111           
  Misses       3089     3089           
  Partials      283      283

---

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[codecov-io]

Codecov Report

Merging #1838 into master will increase coverage by 1.55%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1838      +/-   ##
==========================================
+ Coverage    49.9%   51.45%   +1.55%     
==========================================
  Files         168      171       +3     
  Lines        7354     7690     +336     
==========================================
+ Hits         3670     3957     +287     
- Misses       3328     3357      +29     
- Partials      356      376      +20

Impacted Files	Coverage Δ
pkg/skaffold/deploy/kubectl.go	68.05% <0%> (-6.19%)	⬇️
cmd/skaffold/app/cmd/dev.go	10.09% <0%> (-3.19%)	⬇️
pkg/skaffold/deploy/helm.go	61.92% <0%> (ø)	⬆️
pkg/skaffold/schema/versions.go	65.85% <0%> (ø)	⬆️
pkg/skaffold/event/proto/skaffold.pb.go	5.95% <0%> (ø)	⬆️
pkg/skaffold/schema/v1beta7/config.go
pkg/skaffold/schema/v1beta7/upgrade.go
pkg/skaffold/debug/transform.go	86.2% <0%> (ø)
pkg/skaffold/debug/transform_nodejs.go	82.75% <0%> (ø)
pkg/skaffold/debug/transform_jvm.go	94.84% <0%> (ø)
... and 8 more

---

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Δ = absolute <relative> (impact), ø = not affected, ? = missing data
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[nkubala]

sorry for being grammar police 👮‍♂️

[corneliusweig]

only nits

[balopat]

Thank you so much for taking the lead on this!
First round of nits added. I'll do another round of review soon.

[googlebot]

We found a Contributor License Agreement for you (the sender of this pull request), but were unable to find agreements for all the commit author(s) or Co-authors. If you authored these, maybe you used a different email address in the git commits than was used to sign the CLA (login here to double check)? If these were authored by someone else, then they will need to sign a CLA as well, and confirm that they're okay with these being contributed to Google.
In order to pass this check, please resolve this problem and have the pull request author add another comment and the bot will run again. If the bot doesn't comment, it means it doesn't think anything has changed.

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[googlebot]

We found a Contributor License Agreement for you (the sender of this pull request), but were unable to find agreements for all the commit author(s) or Co-authors. If you authored these, maybe you used a different email address in the git commits than was used to sign the CLA (login here to double check)? If these were authored by someone else, then they will need to sign a CLA as well, and confirm that they're okay with these being contributed to Google.
In order to pass this check, please resolve this problem and have the pull request author add another comment and the bot will run again. If the bot doesn't comment, it means it doesn't think anything has changed.

ℹ️ Googlers: Go here for more info.

[googlebot]

CLAs look good, thanks!

ℹ️ Googlers: Go here for more info.