Fix README table of contents generator title linking

[fevrin]

Background

The table of contents generator does a decent job until it handles a Markdown file with duplicate titles. In that case, the titles' links all point to the same reference, whereas the links for first duplicate title on should have -1, -2, etc. appended to it to properly reference the correct title.

For instance, right now a Markdown file like this:

# Main title

${TOC}

## Subtitle

## Subtitle 2

### Subtitle

### Subtitle 2

#### Subtitle 3

#### Subtitle 2

would get a table of contents like this:

- [Subtitle](#subtitle)
- [Subtitle 2](#subtitle-2)
  - [Subtitle](#subtitle)
  - [Subtitle 2](#subtitle-2)
    - [Subtitle 3](#subtitle-3)
    - [Subtitle 2](#subtitle-2)

instead of this:

- [Subtitle](#subtitle)
- [Subtitle 2](#subtitle-2)
  - [Subtitle](#subtitle-1)
  - [Subtitle 2](#subtitle-2-1)
    - [Subtitle 3](#subtitle-3)
    - [Subtitle 2](#subtitle-2-2)

Definition of Done

• table of contents generator correctly creates links for duplicate titles