Tutorial: Add Step 1 background info and update style

Help/guide/tutorial/Step1/tutorial.cxx

@@ -1,17 +1,22 @@
 // A simple program that computes the square root of a number
 #include <cmath>
-#include <cstdlib>
+#include <cstdlib> // TODO 5: Remove this line
 #include <iostream>
 #include <string>
 
+// TODO 11: Include TutorialConfig.h
+
 int main(int argc, char* argv[])
 {
   if (argc < 2) {
+    // TODO 12: Create a print statement using Tutorial_VERSION_MAJOR
+    //          and Tutorial_VERSION_MINOR
     std::cout << "Usage: " << argv[0] << " number" << std::endl;
     return 1;
   }
 
   // convert input to double
+  // TODO 4: Replace atof(argv[1]) with std::stod(argv[1])
   const double inputValue = atof(argv[1]);
 
   // calculate square root