EDIT: Found the answer;
thks to diego starr;
If anyone is still interested, I finally found out how to import feeds from Google Reader and other apps. For Google Reader, go to Settings and export your subscriptions. The file will download as .xml; change it to .opml so it can be recognized by RSS Hub. Save the .opml file to your device and under New Channel in RSS Hub choose import from PocketPPC and you should be good to go. I'm sure it would be similar for other RSS apps.
EDIT: to save as opml, click save as <all files> and under name of file add <.opml> as the extension.