sfdx-project.json

{
  "packageDirectories": [
    { "path": "sfdx-source/my_ns_prefix", "default": true },
    { "path": "sfdx-source/unpackaged"},
    { "path": "sfdx-source/untracked"}
  ],
  "namespace": "my_ns_prefix",
  "sfdcLoginUrl": "https://login.salesforce.com",
  "sourceApiVersion": "43.0",
  "plugins": {
    "sfdxFalcon": {
      "appxPackage": {
        "schemaVersion"       : "0.0.1",
        "projectName"         : "my-sfdx-falcon-project",
        "projectType"         : "managed-package",
        "namespacePrefix"     : "my_ns_prefix",
        "packageName"         : "My Package Name",
        "metadataPackageId"   : "033000000000000",
        "packageVersionId"    : {
          "stable": "04t000000000000",
          "beta"  : "04t000000000000"
        },
        "gitRemoteUri"        : "https://github.com/my-org/my-repo.git",
        "key3": ["value3a", "value3b", "value3c"],
        "key4": {
          "key4a": "value4a",
          "key4b": "value4b"
        }
      }
    }			
  }  
}