Update validation for addition in permit.rb

There was an issue earlier when nothing is entered on "Size of Addition in Square Feet", the error statement will mention "Addition cannot be larger than 1000 Square Feet", which does not make sense at all.

Now it is fixed, where if addition is not entered, an error message will say "Please enter the size of addition in square feet".

Also changed the statement when 1000 or more is entered, "Addition must be less than 1,000 Square Feet".