Handle multiple folders in the workspace

[jameseogden]

I spent ages with this extension not working because I had multiple folders defined in the workspace eg

myproj.workspace
{
    "folders": [
        {
            "path": "foo"
        },
        {
            "path": "bar"
        },
        {
            "path": "."
        },
}

shell.nix was present in ".". The extension silently didn't find it.

I suggest either

• warning in the log (or the readme even) that there were multiple workspace folders and only the first is checked OR
• enumerate files in each configured folder when building the list of possible environments.

Now it's working, all my intellisense has started working again (I reordered my folders), which is brilliant. Thank you!

[jameseogden]

Obvious dup, sorry.