Make `defaultdict` tag

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diff --git a/bot/resources/tags/defaultdict.md b/bot/resources/tags/defaultdict.md
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+**[`collections.defaultdict`](https://docs.python.org/3/library/collections.html#collections.defaultdict)**
+
+The Python `defaultdict` type behaves almost exactly like a regular Python dictionary, but if you try to access or modify a missing key, the `defaultdict` will automatically create the key and generate a default value for it. 
+While instantiating a `defaultdict`, we pass in a function that tells it how to create a default value for missing keys.
+
+```py
+>>> from collections import defaultdict
+>>> my_dict = defaultdict(int, {"foo": 1, "bar": 2})
+>>> print(my_dict)
+defaultdict(<class 'int'>, {'foo': 1, 'bar': 2})
+```
+
+In this example, we've used the `int` function - this means that if we try to access a non-existent key, it provides the default value of 0.
+
+```py
+>>> print(my_dict["foobar"])
+0
+>>> print(my_dict)
+defaultdict(<class 'int'>, {'foo': 1, 'bar': 2, 'foobar': 0})
+```