[FOSS4G2016] [Program] Changed help text for abstract

[Volker Mische]

Hi LOC, Program Committee,

I changed the text below the abstract text box in the proposal system,
to give guidance on the length of the abstract. It now reads:

    Will be made public if your proposal is accepted. Please aim for
    125-175 words, 250 words is the maximum. Edit using Markdown.

If you propose different numbers for the maximum and aimed for number of
words, let me know. Please keep in mind that you'll probably will read
400 of those abstracts :)

Cheers,
  Volker