docs: Improve headings for changelog.
docs: Improve headings for changelog.

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