Add docs for additional install methods (#1059)

doc/installation_arch.md

@@ -0,0 +1,34 @@
+@page installation_arch Arch Linux
+
+FTXUI is packaged on the AUR. Install using an AUR helper:
+
+```bash
+yay -S ftxui
+```
+
+You can also manually download the PKGBUILD from <https://aur.archlinux.org/packages/ftxui>.
+
+Once installed, you can use it in your CMake projects by adding the following to your `CMakeLists.txt`:
+
+```cmake
+find_package(ftxui REQUIRED)
+add_executable(main main.cpp)
+target_link_libraries(main
+  PRIVATE ftxui::screen
+  PRIVATE ftxui::dom
+  PRIVATE ftxui::component
+)
+```
+
+> [!note]
+> This is an unofficial package. That means it is not maintained by the FTXUI
+> team, but by the community. The package maintainers seems to actively update
+> the package to the latest version. Thanks to the maintainers for their work!
+
+<div class="section_buttons">
+
+| Previous          |
+|:------------------|
+| [Getting Started](getting-started.html) |
+
+</div>