Add code for euclid's algo

chapter-1/notes.org

@@ -1,4 +1,5 @@
 * Euclid's algorithm (Page 2-9)
+** Calculates the greatest common divisor of two numbers.
 ** Definition
 *** E0. [Ensure m >= n.] If m < n, exchange m <-> n.
 *** E1. [Find remainder.] Divide m by n and let r be the remainder.