Updated Tips and tricks (markdown)

Tips-and-tricks.md

@@ -7,14 +7,26 @@ You can use the slanted quote string syntax if you need to use a reserved word a
 ## Tricks with conditional compilation
 
 ```nimrod
-const someFeature = True
-
-when someFeature:
+when defined(useSomeFeature):
   const someSubFeature = true
+  type ID_Type = int32
+  var defaultUserName = "Frank"
 else:
-  const someSubFeature = false
+  type ID_Type = int16
+  var defaultUserName = "Molly"
+
+# `when` does not open a new scope, so `ID_Type` and `defaultUserName`
+# are available here.
+
+when isMainModule:
+  #this code is ran only when this module is the main compilation module
+  echo "This module was compiled on ", CompileDate, " at ", CompileTime
 ```
 
+#### Defining `useSomeFeature`
+* Do it when you compile: `$ nimrod c -d:useSomeFeature myApp`
+* Put it in the local `nimrod.cfg` file `define:useSomeFeature`
+
 ## How do I echo in a ``{.noSideEffects.}`` proc?
 
 You can use ``debugEcho`` for this.