[DOC]: Clear environment version scope

[binmakeswell]

📚 The doc issue

Since we removed the pre-compiled download page, it is currently unclear for users what version of the dependency environment Colossal-AI requires. We should clarify the scope of support, e.g. Python,PyTorch, CUDA, etc. https://colossalai.org/docs/get_started/installation https://github.com/hpcaitech/ColossalAI#Installation