Ability to supply base path (cwd) while using json config

I have two repositories: the first one - with main source code, the second one - with docfx project. I have a CI build which fetches both repos besides and run docfx. So in my docfx.json pathes lead to outside of the current project and depends on folder name of the main repo. I don't want to hard-code it in docfx.json. Instead I want to specify it CLI-argument.

```
{
"metadata": [{
"src": [{
"cwd": "../MainProject/Server.Net", <- this I don't like
"files": [
"WebServer/*.csproj",
],
}],
"dest": "../.tmp/apiserver"
}]
}
```

I run `docfx metadata ./docfx.json`
I want to supply a path to my main repo, i.e. '../MainProject', like
`docfx metadata ./docfx.json --cwd=../MainProject`