Add docs for additional install methods (#1059)

doc/installation_xmake.md

@@ -0,0 +1,40 @@
+@page installation_xmake XMake
+@tableofcontents
+
+## XMake Package (Unofficial)
+
+FTXUI is available in the [xmake-repo](https://github.com/xmake-io/xmake-repo/blob/dev/packages/f/ftxui/xmake.lua)
+
+Example `xmake.lua` snippet:
+
+```lua
+add_requires("ftxui", {system = false})
+
+target("demo")
+    set_kind("binary")
+    add_files("src/*.cpp")
+    add_packages("ftxui")
+```
+
+Refer to the [XMake documentation](https://xmake.io) for further options.
+
+> [!note]
+> This is an **unofficial** package. That means it is not maintained by the FTXUI
+> team, but by the community. 
+
+---
+
+> [!note]
+> The FTXUI author is not very knowledgeable about openSUSE. This page has been
+> mostly generated by AI. If you have any suggestions to improve it, please open
+> a PR.
+
+---
+
+<div class="section_buttons">
+
+| Previous          |
+|:------------------|
+| [Getting Started](getting-started.html) |
+
+</div>