docs: Clarify that the Slack app and API token should be removed.
docs: Clarify that the Slack app and API token should be removed.

hackerkid/zulip,eeshangarg/zulip,eeshangarg/zulip,andersk/zulip,zulip/zulip,kou/zulip,zulip/zulip,andersk/zulip,rht/zulip,punchagan/zulip,zulip/zulip,eeshangarg/zulip,zulip/zulip,eeshangarg/zulip,rht/zulip,punchagan/zulip,zulip/zulip,hackerkid/zulip,kou/zulip,kou/zulip,andersk/zulip,kou/zulip,hackerkid/zulip,punchagan/zulip,eeshangarg/zulip,punchagan/zulip,rht/zulip,andersk/zulip,hackerkid/zulip,punchagan/zulip,rht/zulip,kou/zulip,rht/zulip,andersk/zulip,zulip/zulip,rht/zulip,punchagan/zulip,punchagan/zulip,eeshangarg/zulip,zulip/zulip,eeshangarg/zulip,andersk/zulip,kou/zulip,rht/zulip,hackerkid/zulip,kou/zulip,hackerkid/zulip,hackerkid/zulip,andersk/zulip