Where is the documentation?

In your TeX distribution, the documentation of the class is classified with the documentation of the package cjs-rcs-article. The simplest means to open the English documentation cjs-rcs-article.pdf is through the texdoc utility. From the command line:

texdoc cjs-rcs-article

Most specialized LaTeX editors offer an interface to texdoc. To name a few:

• GNU Emacs: C-c ? or M-x TeX-documentation-texdoc;
• TeXShop: Help | Show Help of Package...;
• texmaker: Help | TexDoc [selection];
• WinEdt: Help | LaTeX Doc.

The documentation is also available online via the interface offered by texdoc.org.

If you opted for a local or manual installation of the class, the documentation resides in your project directory.