Make error message clearer if Node isn't installed (or not found on PATH). Fixes #527

src/Microsoft.AspNetCore.NodeServices/HostingModels/OutOfProcessNodeInstance.cs

@@ -325,6 +325,7 @@ If you haven't yet installed node-inspector, you can do so as follows:
 
         private static Process LaunchNodeProcess(ProcessStartInfo startInfo)
         {
+            try {
                 var process = Process.Start(startInfo);
 
                 // On Mac at least, a killed child process is left open as a zombie until the parent
@@ -336,6 +337,14 @@ If you haven't yet installed node-inspector, you can do so as follows:
                 process.EnableRaisingEvents = true;
 
                 return process;
+            } catch (Exception ex) {
+                var message = "Failed to start Node process. To resolve this:.\n\n"
+                            + "[1] Ensure that Node.js is installed and can be found in one of the PATH directories.\n"
+                            + $"    Current PATH enviroment variable is: { Environment.GetEnvironmentVariable("PATH") }\n"
+                            + "    Make sure the Node executable is in one of those directories, or update your PATH.\n\n"
+                            + "[2] See the InnerException for further details of the cause.";
+                throw new InvalidOperationException(message, ex);
+            }
         }
 
         private static string UnencodeNewlines(string str)