How does one start using Mercurial with an IntelliJ 2017 project?

➠ Am I expected to manually run a `hg init` myself, outside of IntelliJ?

[This Answer to a similar Question](https://stackoverflow.com/a/4282325/642706) suggests “Yes”, but is several years old.

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When I go to IntelliJ > `Settings`/`Preferences` > `Version Control` and set the only item in the list to a value of `Mercurial` in the `VCS` column, and press `Apply` button, I get this error message:

> 
> Invalid VCS root mapping
> 
> 
> The directory is registered as a hg4idea root, but no hg4idea repositories were found there.
> 
> 
>