Is it possible to number the headings in a Google Docs/Drive document?
If you want something more easy, there is a Google Add-On called "Table of Contents" that will allow you to number your headings.
To install this add-on:
Then your Table of Contents should appear in your sidebar. Click on Heading Numbers Format menu, and choose 1.2.3
You have to reformat your document if you have an old one in order to 'refresh' the numbers, but actually the addon works very well.
I've seen the answer in this forum.