Update LibAFL_CC README.md (#1483)

Updated with steps to compile LLVM from source tree

libafl_cc/README.md

@@ -6,3 +6,26 @@ The online documentation for this crate is available [here](https://docs.rs/crat
 
 Currently, we support LLVM version 11 up to 18, but other versions may work.
 To install LLVM, use the official [download page](https://releases.llvm.org/download.html).
+
+The LLVM tools (including clang, clang++) are needed (newer than LLVM 11.0.0 up to LLVM 17.0.0)
+ - When compiling LLVM tools on Windows, you can try to compile LLVM with the below commands (tested on LLVM 16.0.6).
+ - NOTE: This assumes you have Visual Studio 17 2022 and MSVC v143 Tools installed under "Individual Components"
+```sh
+## Start x64 Native Tools Command Prompt for VS 2022
+RUN AS ADMINISTRATOR: %comspec% /k "C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Auxiliary\Build\vcvars64.bat"
+
+## Cloning the LLVM project repo
+git clone https://github.com/llvm/llvm-project.git llvm
+
+## Building Clang project first, the CMAKE_INSTALL_PREFIX is important here, make sure to select a folder path that doesn't contain any spaces in it
+$ cmake -S llvm\llvm -B build -DLLVM_ENABLE_PROJECTS=clang -DLLVM_TARGETS_TO_BUILD=X86 -Thost=x64 -DCMAKE_INSTALL_PREFIX=C:\llvm
+$ cd build
+$ cmake --build . --target install --config release
+
+## Building lld project first, the CMAKE_INSTALL_PREFIX is important here, make sure to select a folder path that doesn't contain any spaces in it
+## Changing back to the previous directory
+$ cd .. 
+$ cmake -S llvm\llvm -B build -DLLVM_ENABLE_PROJECTS=lld -DLLVM_TARGETS_TO_BUILD=X86 -Thost=x64 -DCMAKE_INSTALL_PREFIX=C:\llvm
+$ cd build
+$ cmake --build . --target install --config release
+```