separate setup.py with pip installation, add trouble shooting page

python-package/xgboost/libpath.py

@@ -36,9 +36,10 @@ def find_lib_path():
     else:
         dll_path = [os.path.join(p, 'libxgboostwrapper.so') for p in dll_path]
     lib_path = [p for p in dll_path if os.path.exists(p) and os.path.isfile(p)]
+    #From github issues, most of installation errors come from machines w/o compilers
     if len(lib_path) == 0 and not os.environ.get('XGBOOST_BUILD_DOC', False):
         raise XGBoostLibraryNotFound(
             'Cannot find XGBoost Libarary in the candicate path, ' +
-            'did you run build.sh in root path?\n'
+            'did you install compilers and run build.sh in root path?\n'
             'List of candidates:\n' + ('\n'.join(dll_path)))
     return lib_path