Remind people about the mixer specific steps (#684)
Remind people about the mixer specific steps (#684)

* Remind people about the mixer specific steps

link to dev guide from contributing.md

* mixer -> Mixer per review comment

* opsa... one more

* changing per request

though using "foo-specific" vs "foo specific" isn't so clear (but english isn't my first language so...)


Former-commit-id: 95c81996eee7ce05cb0e1c41221c6f8f55099a63
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