问题： RK3568 Linux terminal 中用python（pip) 无法安装tensorflow：找不到源
硬件： RK3568 dev kit
OS: Ubuntu 18.04 （下载于firefly官网->Core-3568J->Download->Firmware->Ubuntu:http://en.t-firefly.com/doc/download/page/id/89.html）
python: 3.6.9
pip: pip 21.1.2 from /home/firefly/.local/lib/python3.6/site-packages/pip (python 3.6)
具结果如下： （1） firefly@firefly:~$ pip install tensorflow
Defaulting to user installation because normal site-packages is not writeable
ERROR: Could not find a version that satisfies the requirement tensorflow (from versions: none)
ERROR: No matching distribution found for tensorflow
（2） firefly@firefly:~$ python3 -m pip install tensorflow
Defaulting to user installation because normal site-packages is not writeable
ERROR: Could not find a version that satisfies the requirement tensorflow (from versions: none)
ERROR: No matching distribution found for tensorflow