Update the paragraph at the top of the Get Involved page #430

We may want to update the paragraph at the top of the Get Involved page:

Everyone at the University of Waterloo is welcome to come to our events and to use our resources! Feel free to join our communities and chat with our members. However, if you want to officially become a member or support our vision of creating a supportive environment for all computing students, there's a bunch of ways you can join and help out.

In particular:

Who is allowed to attend our events? (Do people need to be MathSoc members? Are social events restricted to CSC members?)
Who is allowed to use what resources? (eg. machines are member-only)
We can probably elaborate slightly on the benefits of membership, either in this paragraph at the top or under the "General Membership" section on this page.