"message.channels" etc. in "Getting Started" guide may be confusing

[seratch]

Description

I've answered this question before: #601 (comment)

While reviewing slackapi/bolt-python#71 , I felt this is confusing (again).

We definitely should have links to the document https://api.slack.com/events/message.channels but we should avoid saying "message.channels" events because actually there is no such event type. My suggestion is to change the label from message.channels to message (in channels) or similar plus to have a link to the event document.

If other maintainers agree with this, we should update Bolt for Python's document as well. As Bolt for Java's one doesn't have this part, we don't have anything to do with it.

What type of issue is this? (place an x in one of the [ ])

• bug
• enhancement (feature request)
• question
• documentation related
• testing related
• discussion

Requirements (place an x in each of the [ ])

• I've read and understood the Contributing guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.
• I've searched for any related issues and avoided creating a duplicate issue.

[seratch]

#757 will be a solution for this issue. Let me close this one.