Added some notes on DLLists.

Author: Clément

source/lectures/data/DLList.md

@@ -16,5 +16,5 @@ The main differences with *singly* linked list are as follows:
 - Instead of keeping only track of the first element (`first`), we keep track of both the first (`head`) and last (`tail`) elements.
 - Each `Cell` contains a pointer to the "next" element (as before), but also to the "previous" element.
 - Adding (or removing) to the right is now done in constant time, instead of linear time.
-- Traversing the list in opposite order (from end to beginning) is now straightforward (cf. the `ToString` method above).
-- The rest of the edits are about bookkeeping the `Previous` and `Next` attributes of the `Cell`, as well as updating the `tail` attribute.
+- Traversing the list in opposite order (from end to beginning, or right to left) is now straightforward (cf. the `ToString` method above).
+- The rest of the edits are about bookkeeping the `Previous` and `Next` attributes of the `Cell`, as well as updating the `tail` attribute. This makes removing and adding "in the middle of the list" a bit tricky.