Add documentation about community plugin

Description

Document the requirement and Process for adding community plugin to the Marketplace.

QA Test Steps

No testing required.

Mana

8

Assignee

Ben Schumacher

QA Assignee

None

Reporter

Ben Schumacher

Epic Link

Fix versions

Mattermost Team

Integrations

Sprint

None

Labels

None

QA Testing Areas

None

GitHub Issue

None

Components

None
Configure