Fix incorrect extra data cheat sheet link

[VojtaStavik]

The link we used in the documentation was incorrect.

[codecov]

Codecov Report

Merging #786 (df23da3) into main (341d4df) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #786   +/-   ##
=======================================
  Coverage   88.59%   88.59%           
=======================================
  Files         218      218           
  Lines        8533     8533           
=======================================
  Hits         7560     7560           
  Misses        973      973           

Impacted Files	Coverage Δ
Sources/StreamChat/ChatClient.swift	95.69% <ø> (ø)
...trollers/ChannelController/ChannelController.swift	91.21% <ø> (ø)
.../ChannelListController/ChannelListController.swift	94.66% <ø> (ø)
.../CurrentUserController/CurrentUserController.swift	95.50% <ø> (ø)
...ontrollers/MemberController/MemberController.swift	97.72% <ø> (ø)
...rs/MemberListController/MemberListController.swift	97.70% <ø> (ø)
...trollers/MessageController/MessageController.swift	95.18% <ø> (ø)
...llers/SearchControllers/UserSearchController.swift	96.03% <ø> (ø)
...at/Controllers/UserController/UserController.swift	97.75% <ø> (ø)
...ollers/UserListController/UserListController.swift	94.36% <ø> (ø)
... and 12 more

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[nuno-vieira]

LGTM