doc: add reference manual

docs/content.en/docs/installation/_index.md

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+title = "installation"
+type  = "docs"
+weight = 1
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+
+# Installation
+
+## Using `single_include`
+
+The `ingle_include/toml.hpp`s is a single-file, header-only library that consolidates all the functionalities of toml11 into one file.
+
+The simplest way to use it is to copy this file to a location included in your `INCLUDE_PATH` and then add `#include <toml.hpp>` to your source code.
+
+The MIT license notice is included in both the comments and the `toml::license_notice()` function.
+If you are redistributing the software without releasing the source code, you must either copy the toml11 license file and include it with your distribution, or ensure that the `toml::license_notice()` function can be called.
+
+## Cloning toml11 and using cmake
+
+If you place toml11 within your repository, for example by using git submodule, and you are using cmake, you can make use of it by adding `add_subdirectory(toml11)` to your `CMakeLists.txt`.
+
+```cmake
+add_subdirectory(toml11)
+add_executable(main main.cpp)
+target_link_libraries(main PUBLIC toml11::toml11)
+```
+
+toml11 will only run tests and install when it is the root project.
+
+## Installing using cmake
+
+After cloning toml11, you can install it using cmake.
+
+```console
+$ cmake -B ./build/ -DTOML11_BUILD_TESTS=ON
+$ cmake --install ./build/ --prefix=/opt/toml11
+```
+
+If you want to run the test programs before installation, make sure to set `-DTOML11_BUILD_TESTS=ON` first.
+
+Once the installation is complete, you can use it as follows:
+
+```cmake
+find_package(toml11)
+add_executable(main main.cpp)
+target_link_libraries(main PRIVATE toml11::toml11)
+```
+
+## Compiling with cmake to Create a Static Library
+
+By defining `-DTOML11_PRECOMPILE=ON` when running cmake, you can precompile some of the functions in toml11, thereby reducing the overall compile time.
+
+```console
+$ cmake -B ./build/ -DTOML11_PRECOMPILE=ON
+```
+
+However, since toml11 supports multiple C++ versions and may switch types based on the value of `__cplusplus`,
+there is a possibility of link failures if the version used during build differs from the version used during usage.
+If you encounter issues, set the required version using `CMAKE_CXX_STANDARD` during compilation.
+If this is difficult, use it as a header-only library as usual.
+
+The `find_package(toml11)` command defines `TOML11_INCLUDE_DIR`.
+Even if you install it as a precompiled library, you can still use it as a header-only library by adding `TOML11_INCLUDE_DIR` to `target_include_directories` and avoiding the use of `target_link_libraries`.
+
+```cmake
+find_package(toml11)
+add_executable(main main.cpp)
+# Include only, do not link
+target_include_directories(main PRIVATE ${TOML11_INCLUDE_DIR})
+```
+
+## Compiling Examples
+
+You can compile the `examples/` directory by setting `-DTOML11_BUILD_EXAMPLES=ON`.
+
+```console
+$ cmake -B ./build/ -DTOML11_BUILD_EXAMPLES=ON
+$ cmake --build ./build/
+```
+
+The executable binaries for the examples will be generated in the `examples/` directory.
+
+## Running Tests
+
+To build the tests, set `-DTOML11_BUILD_TESTS=ON`.
+
+```console
+$ git submodule update --init --recursive
+$ cmake -B ./build/ -DTOML11_BUILD_TESTS=ON
+$ cmake --build ./build/
+$ ctest --test-dir ./build/
+```
+
+To run the `toml-lang/toml-tests`, set `-DTOML11_BUILD_TOML_TESTS=ON`. This will build `toml11_decoder` and `toml11_encoder` in the `tests/` directory.
+
+```console
+$ git submodule update --init --recursive
+$ cmake -B ./build/ -DTOML11_BUILD_TOML_TESTS=ON
+$ cmake --build ./build/
+$ ctest --test-dir ./build/
+```
+