Update install documentation

Noticed that
1) libxkbcommon-x11 dependency wasn't accounted for
2) cd for stardust-client-tests was wrong

docs/getting-started/install.md

@@ -62,6 +62,7 @@ AUR: `stardust-xr-git`
 8. wayland
 9. xwayland
 10. OpenXR Loader (required even if run in flatscreen mode, generally just named `openxr`)
+11. libxkbcommon-x11
 
 ### Download
 ```bash
@@ -96,7 +97,7 @@ meson install --skip-subprojects
 ### Download
 ```bash
 git clone https://github.com/StardustXR/stardust-client-tests.git
-cd stardust-xr
+cd stardust-client-tests
 ```
 
 ### Build
@@ -104,4 +105,4 @@ cd stardust-xr
 meson build --prefix=/usr
 cd build
 ninja
-```
+```