Add instructions of installing dependencies using pip

[gongminmin]

• Enable to support Windows and venv.
• Simplify the installation.

[gongminmin]

The major inspiration is from #3 (comment). The commands are reorganized into requirements files. Due to dependencies, they have to be separated into 2 files.

Other than that, there are 3 differences between that post and this one.

1. wheel is added to build the package in wheel mode. This fixes diffoctreerast and diff-gaussian-rasterization on Python 3.11 and 3.12.
2. Select the whl of flash-attn based on Python version.
3. Change spconv to cu124 to support Python 3.12.