update installation guide for the C++ version

The installation is now possible using cmake

docs/installation.md

@@ -43,5 +43,67 @@ template: overrides/main.html
     ```
 
 === "C++"
-    As of now it it only possible to use the sources directly by adding them to your
-    project. There will be a version on `conan` in the future
+    There are severals ways to integrate `rapidfuzz` in your CMake project.
+
+    ## By Installing it
+    ```bash
+    git clone https://github.com/maxbachmann/rapidfuzz-cpp.git rapidfuzz-cpp
+    cd rapidfuzz-cpp
+    mkdir build && cd build
+    cmake ..
+    cmake --build .
+    cmake --build . --target install
+    ```
+
+    Then in your CMakeLists.txt: 
+    ```cmake
+    find_package(rapidfuzz REQUIRED)
+    add_executable(foo main.cpp)
+    target_link_libraries(foo rapidfuzz::rapidfuzz)
+    ```
+
+    ## Add this repository as a submodule
+    ```bash
+    git submodule add https://github.com/maxbachmann/rapidfuzz-cpp.git 3rdparty/RapidFuzz
+    ```
+    Then you can either:
+
+    1. include it as a subdirectory
+        ```cmake
+        add_subdirectory(3rdparty/RapidFuzz)
+        add_executable(foo main.cpp)
+        target_link_libraries(foo rapidfuzz::rapidfuzz)
+        ```
+    2. build it at configure time with `FetchContent`
+        ```cmake
+        FetchContent_Declare( 
+          rapidfuzz
+          SOURCE_DIR ${CMAKE_SOURCE_DIR}/3rdparty/RapidFuzz
+          PREFIX ${CMAKE_CURRENT_BINARY_DIR}/rapidfuzz
+          CMAKE_ARGS -DCMAKE_INSTALL_PREFIX:PATH=<INSTALL_DIR> "${CMAKE_OPT_ARGS}"
+        )
+        FetchContent_MakeAvailable(rapidfuzz)
+        add_executable(foo main.cpp)
+        target_link_libraries(foo PRIVATE rapidfuzz::rapidfuzz)
+        ```
+    ## Download it at configure time
+
+    If you don't want to add `rapidfuzz-cpp` as a submodule, you can also download it with `FetchContent`:
+    ```cmake
+    FetchContent_Declare(rapidfuzz
+      GIT_REPOSITORY https://github.com/maxbachmann/rapidfuzz-cpp.git
+      GIT_TAG master)
+    FetchContent_MakeAvailable(rapidfuzz)
+    add_executable(foo main.cpp)
+    target_link_libraries(foo PRIVATE rapidfuzz::rapidfuzz)
+    ```
+    It will be downloaded each time you run CMake in a blank folder.   
+
+    ## CMake options
+
+    There are the following CMake options:
+
+    1. `BUILD_TESTS` : to build test (default OFF and requires [Catch2](https://github.com/catchorg/Catch2))
+
+    2. `BUILD_BENCHMARKS` : to build benchmarks (default OFF and requires [Google Benchmark](https://github.com/google/benchmark))
+