add linux install instructions

Install-on-GNU-Linux.md

@@ -0,0 +1,10 @@
+openSUSE Tumbleweed has raylib in the [devel:libraries:c_c++ devel project](https://build.opensuse.org/project/show/devel:libraries:c_c++).
+
+You can easily install it by adding the repository, refreshing your sources and insalling:
+```
+zypper ar -f http://download.opensuse.org/repositories/devel:/libraries:/c_c++/openSUSE_Factory/devel:libraries:c_c++.repo
+zypper ref
+zypper in raylib-devel
+```
+
+If you are a packager for another Distribution, please take the time and create a raylib package.