[trivial][doc] Mention ++i as preferred to i++ in dev notes

doc/developer-notes.md

@@ -14,6 +14,7 @@ gradually.
   - No indentation for public/protected/private or for namespaces.
   - No extra spaces inside parenthesis; don't do ( this )
   - No space after function names; one space after if, for and while.
+  - `++i` is preferred over `i++`.
 
 Block style example:
 ```c++
@@ -24,7 +25,7 @@ class Class
     bool Function(char* psz, int n)
     {
         // Comment summarising what this section of code does
-        for (int i = 0; i < n; i++) {
+        for (int i = 0; i < n; ++i) {
             // When something fails, return early
             if (!Something())
                 return false;