Update docs for site-packages #157

The document states that “By default, Serious Python expects Python dependencies installed into pypackages directory in the root of app directory. You can add additional paths to look for 3rd-party packages using modulePaths parameter”

But in the code，Only Pyodide will use the pypackages folder ？ why??
if (platform != "Pyodide") { if (Platform.environment .containsKey(sitePackagesEnvironmentVariable)) { sitePackagesRoot = Platform.environment[sitePackagesEnvironmentVariable]; } sitePackagesRoot = path.join(tempDir.path, defaultSitePackagesDir); if (sitePackagesRoot == null || sitePackagesRoot.isEmpty) { sitePackagesRoot = path.join(currentPath, "build", "site-packages"); } } else { sitePackagesRoot = path.join(tempDir.path, defaultSitePackagesDir); }