Added note to 1511 2D array problem (#262)

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

* Changed 1511 2D-Malloc Note Order

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Co-authored-by: Liam Smith <tepigtls@outlook.com>

Author: BadAtEveryGame

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

@@ -41,6 +41,7 @@ $ ./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.
+- 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!
 - You do not need to worry about a horrific eldritch abomination destroying your computer midway through runtime.
 
 ## CSE Autotest