Support subdirectories (monorepos)

[matsn0w]

At our company, we have monorepos with roughly this structure:

my-project/
  - api/
    - herd.yml 
    - ...
  - frontend/
    - ...
  - .editorconfig
  - deploy.php 
  - README.md
  - ...

It currently is not possible to place the herd.yml file in the root of the repo. Instead, we have to place it in the api/ folder. This has the side-effect of naming the site as 'api.test' for example.

This could also be useful if, for example, you have a config/ folder or something like that where all configuration files live.

Request: it would be nice if one could configure a (sub)directory in herd.yml to specify where the application lives.

Keep up the good work!