add more examples

doc/examples/counter.fut

@@ -0,0 +1,5 @@
+proc counter() -> Logic<8> {
+	reg count = 8'0;
+	count = count + 1;
+	count
+}

doc/examples/match.fut

@@ -0,0 +1,6 @@
+comb match_not(a: Logic<1>) -> Logic<8> {
+	match (a) {
+		1'1 => 8'10,
+		1'0 => 8'5
+	}
+}