Add tutorial READMEs and fix tutorial return codes

Add README.md files for moeo/tutorial/Lesson{1-4}, smp/tutorial/Lesson{1-4},
and mo/tutorial/Lesson9 — these tutorials had no documentation.

Fix return 1 → return 0 in 28 tutorial main() functions across mo/ and
smp/ that unconditionally returned failure status.

mo/tutorial/Lesson6/sampling.cpp

@@ -252,5 +252,5 @@ int main(int argc, char **argv)
     catch (exception& e) {
         cout << "Exception: " << e.what() << '\n';
     }
-    return 1;
+    return 0;
 }