Usage instructions should mention <-- toc --> marker at the beginning

[dbooth-boston]

It would help if the usage instructions said up front said something like:

1. Add the following line to your markdown file where you want your TOC inserted:
   <-- toc -->
2. Run markdown-toc:
   ...

This information does appear much later in the README.md, but it would help to have it right up front also.

Let me know if I should submit a Pull Request for this.

[doowb]

It's listed in the CLI usage section under the -i flag since it's only used when "inserting" the TOC into the markdown file.

Feel free to submit a PR to clarify this since other people may miss that point too. There could be a "Quick start" section before "CLI" or something like that, that just shows a simple markdown file and the command to run.

---

Quick start

Create a markdown file: README.md

<!-- toc -->
# A

## aa

something in aa

## ab

something in ab

Run the markdown-toc command:

markdown-toc -i README.md

---

Something like that might provide some more information.

[doowb]

This was resolved in #100