feature-request: provide a way to use in the end, e.g. for index

# Purpose

I want to have a short TOC at start, so that people naturally start with a Usage section immediately following it  and a more comprehensive Index in the end with a list of all functions. Here is my [readme](https://github.com/Suor/battle-brothers-stdlib).

# Ideal implementation

Some new option will do the best, i.e. `start = "top"`. Current behavior might be `start = "here"`.
