Add description attribute to ClientUser about pycord

[NeloBlivion]

This will be added, but not to ClientUser; bots do not have descriptions, they use the parent description from their Application.
You may fetch the description through application_info, then we will implement the Edit Current Application endpoint separately.
There will be a future PR that adds many missing routes that we haven't properly implemented.
If you wish to try editing right now, here's an example of how you can go about it:

from discord.http import Route

r = Route("PATCH", "/applications/@me")
payload = {"description": "updated wooo"}
data = await bot.http.request(r, json=payload)

This route returns the updated application info.