Platform: add a note about why emscripten_set_window_title() isn't used.

src/Magnum/Platform/Platform.js.in

@@ -93,6 +93,15 @@ mergeInto(LibraryManager.library, {
         stringToUTF8(id, memory, bytes);
         return memory;
     },
+    /* There's also emscripten_set_window_title(), but this takes an explicit
+       length, allowing the caller to not need to make a null-terminated copy.
+       Sized UTF8ToString() is also used everywhere else in our code, which is
+       better than mixing it with unsized according to Emscripten UTF8ToString()
+       docs:
+
+        N.B. mixing frequent uses of UTF8ToString() with and without
+        maxBytesToRead may throw JS JIT optimizations off, so it is worth to
+        consider consistently using one */
     magnumPlatformSetWindowTitle__deps: [
         ${MagnumPlatform_EMSCRIPTEN_3135_ONLY} '$UTF8ToString'
     ],