Keep ascii art for shell usage

Author: habere-et-dispertire

exercises/binary-search-tree/description.md

@@ -21,18 +21,47 @@ For example, if we had a node containing the data 4, and we added the data 2, ou
 
 ![A graph with root node 4 and a single child node 2.](https://assets.exercism.org/images/exercises/binary-search-tree/tree-4-2.svg)
 
+```text
+      4
+     /
+    2
+```
+
 If we then added 6, it would look like this:
 
 ![A graph with root node 4 and two child nodes 2 and 6.](https://assets.exercism.org/images/exercises/binary-search-tree/tree-4-2-6.svg)
 
+```text
+      4
+     / \
+    2   6
+```
+
 If we then added 3, it would look like this
 
 ![A graph with root node 4, two child nodes 2 and 6, and a grandchild node 3.](https://assets.exercism.org/images/exercises/binary-search-tree/tree-4-2-6-3.svg)
 
+```text
+       4
+     /   \
+    2     6
+     \
+      3
+```
+
 And if we then added 1, 5, and 7, it would look like this
 
 ![A graph with root node 4, two child nodes 2 and 6, and four grandchild nodes 1, 3, 5 and 7.](https://assets.exercism.org/images/exercises/binary-search-tree/tree-4-2-6-1-3-5-7.svg)
 
+```text
+          4
+        /   \
+       /     \
+      2       6
+     / \     / \
+    1   3   5   7
+```
+
 ## Credit
 
 The images were created by [habere-et-dispertire][habere-et-dispertire] using [PGF/TikZ][pgf-tikz] by Till Tantau.