fix unix permissions with chmod examples

Example 1: chmod

chmod u=rwx,g=rx,o=r myfile

chmod 754 myfile

# 4 stands for "read",
# 2 stands for "write",
# 1 stands for "execute", and
# 0 stands for "no permission."

Example 2: chmod values

The three rightmost digits define permissions for the:
file user, the group, and others. 

Example usage: sudo chmod 777 testfile.txt

#	Permission				rwx	Binary
7	read, write and execute	rwx	111
6	read and write			rw-	110
5	read and execute		r-x	101
4	read only				r--	100
3	write and execute		-wx	011
2	write only				-w-	010
1	execute only			--x	001
0	none					---	000