`-i` option doesn't work as expected

[skywinder]

Steps to reproduce:

markdown-toc -i README.md - produce 0 input, readme file doesn't change.

I thought it syntax issue, tried: markdown-toc -i README.md README.md - return help message.

Expected result: README.md shoud be injected with toc section.

[doowb]

Does your README.md have a <!-- toc --> html comment? See this example in the README.md.