cpu install guide (#1227)

* cpu install guide

* update readme

* fix format

* fix format

* fix typo

* add windows guide

* fix readme to pip install . instead of building wheel

* Update docs/source/installation.mdx
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

* Update docs/source/installation.mdx
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

* Update docs/source/installation.mdx
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

---------
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

docs/source/installation.mdx

 # Installation
 
+## CUDA
+
 bitsandbytes is only supported on CUDA GPUs for CUDA versions **11.0 - 12.3**.
 
 The latest version of bitsandbytes (v0.43.0) builds on:
@@ -29,7 +31,7 @@ To install from PyPI.
 pip install bitsandbytes
 ```
 
-## Compile from source
+### Compile from source
 
 For Linux and Windows systems, you can compile bitsandbytes from source. Installing from source allows for more build options with different CMake configurations.
 
@@ -91,7 +93,7 @@ Big thanks to [wkpark](https://github.com/wkpark), [Jamezo97](https://github.com
 </hfoption>
 </hfoptions>
 
-## PyTorch CUDA versions
+### PyTorch CUDA versions
 
 Some bitsandbytes features may need a newer CUDA version than the one currently supported by PyTorch binaries from Conda and pip. In this case, you should follow these instructions to load a precompiled bitsandbytes binary.
 
@@ -131,3 +133,51 @@ export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/home/tim/local/cuda-11.7
 ```
 
 3. Now when you launch bitsandbytes with these environment variables, the PyTorch CUDA version is overridden by the new CUDA version (in this example, version 11.7) and a different bitsandbytes library is loaded.
+
+
+## Intel CPU
+
+> [!TIP]
+> Intel CPU backend only supports building from source; for now, please follow the instructions below.
+
+Like CUDA, you can compile bitsandbytes from source for Linux and Windows systems. Installing from source allows for more build options with different CMake configurations.
+
+<hfoptions id="source">
+<hfoption id="Linux">
+
+To compile from source, you need CMake >= **3.22.1** and Python >= **3.8** installed. Make sure you have a compiler installed to compile C++ (gcc, make, headers, etc.). For example, to install a compiler and CMake on Ubuntu:
+
+```bash
+apt-get install -y build-essential cmake
+```
+
+We recommend installing **GCC >= 11** and have at least **GCC >= 6**.
+
+Now to install the bitsandbytes package from source, run the following commands:
+
+```bash
+git clone --branch multi-backend-refactor https://github.com/TimDettmers/bitsandbytes.git && cd bitsandbytes/
+pip install -r requirements-dev.txt
+pip install intel_extension_for_pytorch
+cmake -DCOMPUTE_BACKEND=cpu -S .
+make
+pip install .
+```
+
+</hfoption>
+<hfoption id="Windows">
+
+Windows systems require Visual Studio with C++ support.
+
+To compile from source, you need CMake >= **3.22.1** and Python >= **3.8** installed.
+
+```bash
+git clone --branch multi-backend-refactor https://github.com/TimDettmers/bitsandbytes.git && cd bitsandbytes/
+pip install -r requirements-dev.txt
+cmake -DCOMPUTE_BACKEND=cpu -S .
+cmake --build . --config Release
+pip install .
+```
+
+</hfoption>
+</hfoptions>