Automatically open readme file after generating project

Most project templates hold a readme file, which provides instructions on how to run the generated project, etc. After generating the project, we want to automatically open the readme, so that users know which next steps they need to take.

We could implement this by placing a special file, like `.confluent-version` or similar, in the generated project, which triggers extension activation. Upon detecting this file in the workspace, the extension could then open the readme file.