Put example in API/__ini__

mapytex/calculus/API/__init__.py

@@ -7,6 +7,31 @@
 # Distributed under terms of the MIT license.
 
 """
+Generate and compute like a student!
+
+:example:
+
+>>> e = Expression.from_str("2+3*4")
+>>> e_simplified = e.simplify()
+>>> print(e_simplified)
+14
+>>> for s in e_simplified.explain():
+...    print(s)
+2 + 3 * 4
+2 + 12
+14
+>>> e = Expression.from_str("2+3/2")
+>>> e_simplified = e.simplify()
+>>> print(e_simplified)
+7 / 2
+>>> for s in e_simplified.explain():
+...    print(s)
+2 + 3 / 2
+2 / 1 + 3 / 2
+(2 * 2) / (1 * 2) + 3 / 2
+4 / 2 + 3 / 2
+(4 + 3) / 2
+7 / 2
 
 """