Hello,

GNU Webmasters are planning to migrate all templated pages (those
using SSIs) to HTML5 in order to improve accessibility. But before
doing this, deprecated tags such as <tt>, <acronym> and <big> need
to be removed.

The home page of ACM contains <tt> in the Mailing lists section.
I got rid of it, and took this opportunity to do some minor edits:

• Download: reword to avoid long URLs in the text (very bothersome

  for screen reader users).

• Documentation: list the manual first; use <ul>; replace <em> with

  <kbd> (command) or <code> (directory).

• Mailing lists: reword more concisely; replace <tt> with quotes.
• Get involved: remove the commented-out part, Test releases

  (obsolete), and subheadings.

• http > https.
• Wrap long lines.
• Boilerplate update.

A diff is attached. If you agree with the changes but don't have time
to commit them right now, I will gladly do it.

Best regards,
Thérèse