Add upgrade instructions to the README

Author: abetlen

README.md

@@ -28,6 +28,12 @@ pip install llama-cpp-python
 The above command will attempt to install the package and build build `llama.cpp` from source.
 This is the recommended installation method as it ensures that `llama.cpp` is built with the available optimizations for your system.
 
+If you have previously installed `llama-cpp-python` through pip and want to upgrade your version or rebuild the package with different  compiler options, please add the following flags to ensure that the package is rebuilt correctly:
+
+```bash
+pip install llama-cpp-python --force-reinstall --upgrade --no-cache-dir
+```
+
 Note: If you are using Apple Silicon (M1) Mac, make sure you have installed a version of Python that supports arm64 architecture. For example:
 ```
 wget https://github.com/conda-forge/miniforge/releases/latest/download/Miniforge3-MacOSX-arm64.sh