Add missing class docstrings in Downloader, Reports and Streams (#3892)

* add class docstring to downloader

idk what to say rly
um hi all nice to be back after about 6 months
pls no hate my PRs
apoligies if i get in the way
if you read this far then you deserve an achievement um i dunno what err how about the achievement of unboredness

* add class docstring to reports

* add class docstring to streams

* black formatting

oops lets not forget what tox checks for

* wording changes

* add cog board link

* hmm actually no (undo)

* wait grammar exists? who knew...

* remove admin only commands

* Review

* Remove always
  - and consequently reorganise the words
* Add "one or more"
* Fix spelling of creator
  - changed from creater

redbot/cogs/downloader/downloader.py

@@ -36,6 +36,17 @@ DEPRECATION_NOTICE = _(
 
 @cog_i18n(_)
 class Downloader(commands.Cog):
+    """Install community cogs made by Cog Creators.
+
+    Community cogs, also called third party cogs, are not included
+    in the default Red install.
+    
+    Community cogs come in repositories. Repos are a group of cogs
+    you can install. You always need to add the creator's repository
+    using the `[p]repo` command before you can install one or more
+    cogs from the creator.
+    """
+
     def __init__(self, bot: Red):
         super().__init__()
         self.bot = bot