Fix broken link in speaker biography help text.

[martey]

This has been broken since 36ab6d599ffca01b83d5a93a2b5b7fa6b5bd9d70.

[jhrr]

Thanks very much for the fix. While we're at it, I think a multi-line string and some formatting changes like the following would make things a bit more readable and manageable here:

biography = models.TextField(
    blank=True,
    help_text=_(
        """A little bit about you. Edit using <a
        href='http://warpedvisions.org/projects/markdown-cheat-sheet/'
        target='_blank'>Markdown</a>."""
    ),
    verbose_name=_("Biography")
)

[jhrr]

Or if not the triple quotes then at least something like this?

biography = models.TextField(
    blank=True,
    help_text=_(
        "A little bit about you. Edit using"
        "<a href='http://warpedvisions.org/projects/markdown-cheat-sheet/'target='_blank'>"
        "Markdown</a>."
    ),
    verbose_name=_("Biography")
)

[martey]

I've updated the formatting and changed to the link to use HTTPS.