[Doc] Extend the README with installation instructions

docs/build_options.md

@@ -28,3 +28,189 @@ Building the CoSimIO with the following configuration:
     CO_SIM_IO_BUILD_FORTRAN:   ON
     CO_SIM_IO_STRICT_COMPILER: ON
 ~~~
+
+## Installation
+
+### Manual Installation
+
+If you prefer not to use Spack, _CoSimIO_ can be built and installed manually using [CMake](https://cmake.org/).
+
+#### Prerequisites
+
+- A C++11 compatible compiler (GCC, Clang, MSVC, etc.) — see the full list [here](https://en.cppreference.com/w/cpp/compiler_support#cpp11)
+- [CMake](https://cmake.org/) ≥ 3.15
+- _(Optional)_ An MPI implementation (e.g. [OpenMPI](https://www.open-mpi.org/), [MPICH](https://www.mpich.org/)) for `+mpi` support
+- _(Optional)_ [Python](https://www.python.org/) ≥ 3.6 and [pybind11](https://github.com/pybind/pybind11) for Python bindings
+- _(Optional)_ A Fortran compiler for the Fortran API
+
+#### 1. Clone the Repository
+
+```bash
+git clone https://github.com/KratosMultiphysics/CoSimIO.git
+cd CoSimIO
+```
+
+Or download a specific release tarball:
+
+```bash
+wget https://github.com/KratosMultiphysics/CoSimIO/archive/refs/tags/v4.3.1.tar.gz
+tar -xzf v4.3.1.tar.gz
+cd CoSimIO-4.3.1
+```
+
+#### 2. Configure with CMake
+
+Create a build directory and run CMake:
+
+```bash
+mkdir build && cd build
+cmake ..
+```
+
+The following CMake options are available to control what gets built:
+
+| CMake Option | Default | Description |
+|---|---|---|
+| `CO_SIM_IO_BUILD_C` | `ON` | Build the C API |
+| `CO_SIM_IO_BUILD_PYTHON` | `OFF` | Build Python bindings |
+| `CO_SIM_IO_BUILD_FORTRAN` | `OFF` | Build the Fortran API |
+| `CO_SIM_IO_BUILD_TESTING` | `OFF` | Build the test suite |
+| `CO_SIM_IO_BUILD_MPI` | `OFF` | Enable MPI communication |
+| `CO_SIM_IO_STRICT_COMPILER` | `OFF` | Enable strict compiler warnings |
+
+For example, to enable MPI and Python bindings:
+
+```bash
+cmake .. \
+    -DCMAKE_BUILD_TYPE=Release \
+    -DCO_SIM_IO_BUILD_MPI=ON \
+    -DCO_SIM_IO_BUILD_PYTHON=ON
+```
+
+To specify a custom install prefix:
+
+```bash
+cmake .. -DCMAKE_INSTALL_PREFIX=/path/to/install
+```
+
+> **Note:** The Fortran API depends on the C API. Always enable `CO_SIM_IO_BUILD_C=ON` when building with `CO_SIM_IO_BUILD_FORTRAN=ON`.
+
+#### 3. Build
+
+```bash
+cmake --build . --config Release
+```
+
+To speed up compilation using multiple cores:
+
+```bash
+cmake --build . --config Release -- -j$(nproc)
+```
+
+> On macOS, replace `$(nproc)` with `$(sysctl -n hw.logicalcpu)`.
+
+#### 4. Install
+
+```bash
+cmake --install .
+```
+
+If a custom prefix was specified during configuration, the libraries and headers will be placed there. Otherwise the default system prefix (e.g. `/usr/local`) is used.
+
+#### 5. Verify the Installation
+
+After installation, confirm that the shared library is present:
+
+```bash
+ls /path/to/install/lib/libCoSimIO*
+```
+
+If Python bindings were built, verify the module is importable (defining properly the `PYTHONPATH`):
+
+```bash
+python3 -c "import CoSimIO; print('CoSimIO imported successfully')"
+```
+
+#### Platform-Specific Notes
+
+| Platform | Notes |
+|---|---|
+| **Linux** | Ensure `/path/to/install/lib` is on `LD_LIBRARY_PATH` |
+| **macOS** | Ensure `/path/to/install/lib` is on `DYLD_LIBRARY_PATH` |
+| **Windows** | Ensure `/path/to/install/bin` is on `PATH`; use the Visual Studio generator with `-G "Visual Studio 17 2022"` |
+
+### Installing with Spack
+
+This section describes how to install _CoSimIO_ using [Spack](https://spack.io/), a flexible package manager designed for HPC environments. First, make sure Spack is available in your environment:
+
+```bash
+git clone --depth=1 https://github.com/spack/spack.git
+source spack/share/spack/setup-env.sh
+```
+
+Then install _CoSimIO_ with the default configuration:
+
+```bash
+spack install cosimio
+```
+
+### Variants
+
+The Spack package exposes several build variants that allow you to tailor the installation to your needs:
+
+| Variant | Default | Description |
+|---|---|---|
+| `+mpi` / `~mpi` | `~mpi` | Enable MPI-parallel communication |
+| `+c` / `~c` | `+c` | Build the C API |
+| `+python` / `~python` | `~python` | Build Python bindings (requires Python ≥ 3.6) |
+| `+fortran` / `~fortran` | `~fortran` | Build the Fortran API (requires `+c`) |
+| `+testing` / `~testing` | `~testing` | Build the test suite |
+| `+strict` / `~strict` | `~strict` | Enable strict compiler warnings |
+
+> **Note:** The Fortran API is built on top of the C API. Enabling `+fortran` without `+c` is not allowed.
+
+#### Examples
+
+Install with MPI support:
+
+```bash
+spack install cosimio+mpi
+```
+
+Install with Python bindings:
+
+```bash
+spack install cosimio+python
+```
+
+Install with C, Fortran, and MPI support:
+
+```bash
+spack install cosimio+c+fortran+mpi
+```
+
+Install a specific version:
+
+```bash
+spack install cosimio@4.3.1
+```
+
+### Loading the Package
+
+Once installed, load _CoSimIO_ into your environment with:
+
+```bash
+spack load cosimio
+```
+
+### Dependencies
+
+Spack resolves all dependencies automatically. For reference, the following are pulled in depending on the chosen variants:
+
+| Dependency | When required |
+|---|---|
+| `cmake@3.15:` | Always (build only) |
+| `mpi` | `+mpi` |
+| `python@3.6:` | `+python` |
+| `py-pybind11` | `+python` (build only) |
+| Fortran compiler | `+fortran` |