[docs] [issue14112] tutorial intro talks of "shallow copy" concept without explanation

Change by Raymond Hettinger <raymond.hettinger@gmail.com>: ---------- pull_requests: +15113 pull_request: https://github.com/python/cpython/pull/15408 _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue14112> _______________________________________