Create NeedlemanWunsch.py

[farahzk]

This version takes two input files along with a similarity score matrix and gap penalty through terminal/command line

[alevchuk]

sounds good, i'm ready to accept this, but one small nit:

for readability, please assign all argv[...] to variables at the beginning of the program, e.g.:
fasta_file_one = sys.argv[1]
fasta_file_two = sys.argv[2]
substitution_matrix_file = sys.argv[3]
gap_penalty = sys.argv[4]

and then use the variables in the code.