If you already bought the asset on the asset store and either want to participate in beta testing, or just follow the development more closely, you can get access to complete git repository and issue tracking here.
First you have to register on gitlab.com, if you haven't done so already. It's totally free and similar to github or bitbucket.
Then you can send me your gitlab username and Pre-Integrated Skin Shader invoice (either pdf or just the invoice number).
Then I'll give you access to the repository, which you can access here.
When downloading from git repository keep in mind that it's the code I may be actively working on. Things may brake occasionally and features may get added or removed based on my mood swings.
Downloading from git repository
If you're not a programmer or otherwise don't have any git experience, don't panic!
All you need to do is to "clone" the repository. That just means downloading all the files together with the development history.
First you need a git client. For example source tree.
Install it, and then, perform a clone. You just need to provide the repository url, https://gitlab.com/jbrothers/pre-integrated-skin-shader.git, your gitlab account and password, and the local path to download. Then relax for a bit, since it can take a while.
To download the latest changes you "pull" them.
If you don't have any local changes this should work flawlessly. Otherwise, inevitably you'll get conflicts and the pull command will fail. At this stage, you either deep dive into git and learn how to manage conflicts, or just hard-reset your local changes before pull like this. Beware that this will destroy your local changes!
If you have any problems, let me know so I can improve this little guide.
If you're already registered on gitlab and granted "reporter" access to the repository you can fill an issue directly. Otherwise send me a mail or write on the official forum thread.