You can hit the Enter/Return key on your keyboard to add a newline to your text:
Append, '[[{INT:textCapIndex}]] [ {TIME} ] [ {DATE} ] [[[[ {CLIP} ]]]]
' to file 'C:\VAOutput.txt'
Note that this does mean the last line in the file will be empty. The alternative is to add the newline before your text, but then the first line will be empty. Take your pick.