readme: Add initial readme file

README.md

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+# PPPlugin
+
+[!WARNING]
+Until version 1.0.0 is released, all interfaces and features are subject
+to change and there are no guarantees regarding stability.
+
+This library aims to provide an easy-to-use and modern C++ interface
+to extend an existing library at runtime via plugins.
+
+These plugins can be written in C++, C, Lua and Python.
+All languages share, once loaded, the same interface and can be used
+interchangeably.
+
+## Usage
+
+```cmake
+# set(PPPLUGIN_SHARED ON) # uncomment to use shared instead of static library
+find_package(ppplugin REQUIRED)
+
+target_link_library(<target> ppplugin::ppplugin)
+```
+
+For code usage, please refer to the different examples in `examples/`.
+
+## Compilation
+
+To build the repository with default options, run the following commands:
+
+```console
+cmake . -B build
+cmake --build build -j
+cmake --install build --prefix build/root/usr/local
+```
+
+This will compile and install the library to the directory `build/root`.
+
+Available compilation options:
+
+| Name                       |Default| Description                              |
+| -------------------------- | ----- | ---------------------------------------- |
+| `PPPLUGIN_SHARED`          | `OFF` | Compile as shared library                |
+| `PPPLUGIN_ENABLE_COVERAGE` | `OFF` | Enable flags for measuring test coverage |
+| `PPPLUGIN_ENABLE_TESTS`    | `OFF` | Tests in `tests` will be compiled        |
+| `PPPLUGIN_ENABLE_EXAMPLES` | `OFF` | Examples in `examples` will be compiled  |
+| `DPPPLUGIN_ENABLE_CPP17_COMPATIBILITY` | `OFF` |                              |
+||| Library will be compiled with C++17 compatibility                           |
+
+Extend the first command above with the desired options, for example:
+
+```console
+cmake . -B build -G Ninja \
+  -DCMAKE_BUILD_TYPE=Debug \
+  -DPPPLUGIN_SHARED=ON \
+  -DPPPLUGIN_ENABLE_EXAMPLES=ON \
+  -DPPPLUGIN_ENABLE_TESTS=ON \
+  -DPPPLUGIN_ENABLE_CPP17_COMPATIBILITY=ON
+```