Added clip creation support 🎬 (#2271)

You can create clips with `/clip` command, `Alt+X` keybind or `Create a clip` option in split header's context menu. This requires a new authentication scope so re-authentication will be required to use it.

Co-authored-by: Leon Richardt <leon.richardt@gmail.com>
Co-authored-by: pajlada <rasmus.karlsson@pajlada.com>

src/providers/twitch/api/README.md

@@ -90,7 +90,7 @@ URL: https://dev.twitch.tv/docs/api/reference#get-streams
      * `NotificationController` to provide notifications for channels you might not have open in Chatterino, but are still interested in getting notifications for
 
 ### Follow User
-URL: https://dev.twitch.tv/docs/api/reference#create-user-follows
+URL: https://dev.twitch.tv/docs/api/reference#create-user-follows  
 Requires `user:edit:follows` scope
 
  * We implement this in `providers/twitch/api/Helix.cpp followUser`
@@ -99,7 +99,7 @@ Requires `user:edit:follows` scope
      * `controllers/commands/CommandController.cpp` in /follow command
 
 ### Unfollow User
-URL: https://dev.twitch.tv/docs/api/reference#delete-user-follows
+URL: https://dev.twitch.tv/docs/api/reference#delete-user-follows  
 Requires `user:edit:follows` scope
 
  * We implement this in `providers/twitch/api/Helix.cpp unfollowUser`
@@ -107,6 +107,14 @@ Requires `user:edit:follows` scope
      * `widgets/dialogs/UserInfoPopup.cpp` to unfollow a user by unticking follow checkbox in usercard
      * `controllers/commands/CommandController.cpp` in /unfollow command
 
+### Create Clip
+URL: https://dev.twitch.tv/docs/api/reference#create-clip  
+Requires `clips:edit` scope
+
+ * We implement this in `providers/twitch/api/Helix.cpp createClip`
+   Used in:
+     * `TwitchChannel` to create a clip of a live broadcast
+
 ## TMI
 The TMI api is undocumented.