fix: added a disclaimer note to the 2D malloc exercise regarding it not being a 'true' 2d array

Author: Daniel Chen

data/course-revision/1511-23T3/2d_malloc.mdx

@@ -42,6 +42,7 @@ $ ./2d_malloc 10 10
 - You may assume there is enough memory to allocate the array on the heap.
 - You may **not** store the arrays on the stack.
 - You do not need to worry about a horrific eldritch abomination destroying your computer midway through runtime.
+- Note that this is not a "true" 2D array, but rather a 1D array pointing to 1D arrays. There are slight differences (e.g. it is not stored contiguously in memory), but you don't need to worry about this, it can be "used as" a 2D array!
 
 ## CSE Autotest