docs: add example scheme programs

examples/tailloop.scm

@@ -0,0 +1,20 @@
+; Deep tail recursion: counting to a large number must not overflow the stack.
+(define (count-up n)
+  (let loop ((i 0))
+    (if (= i n)
+        i
+        (loop (+ i 1)))))
+
+(display "counted to ")
+(display (count-up 1000000))
+(newline)
+
+; Mutual tail recursion should also stay in constant stack space.
+(define (even-loop n)
+  (if (= n 0) #t (odd-loop (- n 1))))
+(define (odd-loop n)
+  (if (= n 0) #f (even-loop (- n 1))))
+
+(display "even? 1000000 -> ")
+(display (even-loop 1000000))
+(newline)