restrict platform to Linux only since it use ps command

setup.py

@@ -6,11 +6,11 @@ setup(
     keywords='gpu utils',
     description = 'A tool for observing gpu stat and auto set visible gpu in python code.',
     license = 'MIT License',
-    url = '',
+    url = 'https://git.zmy.pub/zmyme/gpuutil',
     author = 'zmy',
     author_email = 'izmy@qq.com',
     packages = find_packages(),
     include_package_data = True,
-    platforms = 'any',
+    platforms = 'Linux',
     install_requires = [],
 )