fixed typo in documentation.

docs/commands.md

 # Enabled NSFW commands
 ;nsfw enable
 # Add "test" as a blacklisted tag
-;nsfw addbagtag test
+;nsfw addbadtag test
 # Remove "Roxbot" as a blacklisted tag
 ;nsfw removebadtag Roxbot
 ```

roxbot/cogs/nsfw.py

 			# Enabled NSFW commands
 			;nsfw enable
 			# Add "test" as a blacklisted tag
-			;nsfw addbagtag test
+			;nsfw addbadtag test
 			# Remove "Roxbot" as a blacklisted tag
 			;nsfw removebadtag Roxbot
 		"""