Clarify "zero-padding" in page image guidelines

[sylvieed]

The "Page Image Guidelines" in the "Start A Project" page mentions "zero-padding", meaning that single-digit numbers should have a 0 in front of them. There's an example to explain this, but some users might still be confused by the term.

We should clarify this.

[kvaithin]

Would the following work.

From:

 (This may require "zero-padding" 
for any page numbers: <code>page_09.jpg, page_10.jpg</code> will sort correctly, ...

To:

 (Need to add a 0 before single digit numbers 
for any page numbers: <code>page_09.jpg, page_10.jpg</code> will sort correctly, ...

[saracarl]

@symmetrically 's numeric ordering fix solves this issue. We should update/remove the message and then close this out.