Add a doc for installation (#128)

docs/source/getting_started/installation.rst

 Installation
 ============
 
+CacheFlow is a Python library that includes some C++ and CUDA code.
+CacheFlow can run on systems that meet the following requirements:
+
+* OS: Linux
+* Python: 3.8 or higher
+* CUDA: 11.0 -- 11.8
+* GPU: compute capability 7.0 or higher (e.g., V100, T4, RTX20xx, A100, etc.)
+
+.. note::
+    As of now, CacheFlow does not support CUDA 12.
+    If you are using Hopper or Lovelace GPUs, please use CUDA 11.8.
+
+.. tip::
+    If you have trouble installing CacheFlow, we recommend using the NVIDIA PyTorch Docker image.
+
+    .. code-block:: console
+
+        $ docker run --gpus all -it --rm --shm-size=8g nvcr.io/nvidia/pytorch:22.12-py3
+
+Install with pip
+----------------
+
+You can install CacheFlow using pip:
+
+.. code-block:: console
+
+    $ # (Optional) Create a new conda environment.
+    $ conda create -n myenv python=3.8 -y
+    $ conda activate myenv
+
+    $ # Install CacheFlow.
+    $ pip install cacheflow
+
+
+.. _build_from_source:
+
 Build from source
 -----------------
 
+You can also build and install CacheFlow from source.
+
 .. code-block:: console
 
+    $ git clone https://github.com/WoosukKwon/cacheflow.git
+    $ cd cacheflow
     $ pip install -r requirements.txt
-    $ pip install -e .  # This may take several minutes.
+    $ pip install -e .  # This may take 5-10 minutes.