Currently there are issues with publishing the extension on the Chrome Web Store. Firstly it was rejected because it “did not comply with their policy” without clear explanation, then it was going through the compliance review for a few business days, then it was published, and now it's finally taken down again. I find that ridiculous.
So, installation is currently possible as follows: get the geekmarks.crx file, Chrome will complain that installing extensions from this website is not allowed, and will just save geekmarks.crx into your Downloads folder. Then, navigate to chrome://extensions/ (you have to copy-paste this URL, sorry), drag-n-drop your previously saved geekmarks.crx file there, and confirm the installation.
I really hope that the issues with publishing to the Chrome Web Store will be resolved soon, so that the installation will be easier.