Added a note in .gitignore to discourage pull requests containing IDE specific files.

.gitignore

@@ -1,3 +1,7 @@
+# If you need to exclude files such as those generated by an IDE, use
+# $GIT_DIR/info/exclude or the core.excludesFile configuration variable as
+# described in https://git-scm.com/docs/gitignore
+
 *.egg-info
 *.pot
 *.py[co]