Write a shell script and it will return the area of an
equilateral triangle. The script will ask for a number to
read from input as the length of sides, then it will
display the output "The area of the equilateral triangle
with side length xx is: xxx" (remain 3 digits after
decimal point). As we known the area of an equilateral
triangle should be V3a?/4, where a is the side length