Add contributing page

[lucas-zimerman]

This will help new folks to better knows how the SDK works and what you need to do to setup it up locally.

[lucas-zimerman]

Additionally, apply the changes done here getsentry/sentry-dotnet#1605 on contributing.

[github-actions]

This issue has gone three weeks without activity. In another week, I will close it.

But! If you comment or otherwise update it, I will reset the clock, and if you label it Status: Backlog or Status: In Progress, I will leave it alone ... forever!

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"A weed is but an unloved flower." ― Ella Wheeler Wilcox 🥀

[lucas-zimerman]

the status in Backlog 🤔

[lucas-zimerman]

Close as completed