Add Supplemental Developer Contribution Guidelines

[xuemingdi]

• Please check if the PR fulfills these requirements

• [x] The commit message follows our guidelines
• [ ] Tests for the changes have been added (for bug fixes / features)
• [x] Docs have been added / updated (for bug fixes / features)

Which issue(s) this PR fixes:

Fixes #

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...) docs update

• What is the current behavior? (You can also link to an open issue here) N.A

• What is the new behavior (if this is a feature change)? Add Supplemental Developer Contribution Guidelines https://github.com/kubeedge/website/issues/585

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?) No.

• Other information:

[kubeedge-bot]

Welcome @xuemingdi! It looks like this is your first PR to kubeedge/website 🎉

[wbc6080]

Could you consider placing this file to https://kubeedge.io/docs/category/developer-guide? @wbc6080

Good idea, @xuemingdi could you help create a new directory under the Developer Guide of https://kubeedge.io/docs/category/developer-guide and copy this part? This part in website will serve as a code submission guide for all kubeedge repos. Some expressions may need to be modified.

[kubeedge-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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