Clarify roles for guest editor recruitment

[noamross]

A few lines specifying what the Software Review Lead and Editor in Chief do in the case of bringing on a guest editor.

[noamross]

Also make sure EiC has appropriate permissions needed to onboard new and guest editors. (@adamhsparks, let's track missing permissions/steps here)

[maelle]

or, a way to request staff members to do so on their behalf. Less bureaucratic work for volunteers 😸

[maelle]

• Create a private slack channel named #guest-editor-<package-name>
• Invite editors to it
• Get name recs from archived similar slack channel
• After a decision has been reached and a guest editor has accepted, archive the channel

[maelle]

@mpadge could I assign this issue to you?