The Org Num minor mode, toggled with M-x org-num-mode, displays outline numbering on top of headlines. It also updates it automatically upon changes to the structure of the document.
By default, all headlines are numbered. You can limit numbering to
specific headlines according to their level, tags, ‘COMMENT’ keyword,
or ‘UNNUMBERED’ property. Set org-num-max-level,
org-num-skip-tags, org-num-skip-commented,
org-num-skip-unnumbered, or org-num-skip-footnotes accordingly.
If org-num-skip-footnotes is non-nil, footnotes sections (see
Creating Footnotes) are not numbered either.
You can control how the numbering is displayed by setting
org-num-face and org-num-format-function.
You can also turn this mode globally for all Org files by setting the
option org-startup-numerated to ‘t’, or locally on a file by using
‘#+startup: num’.