docs: add package availability notes

docs/install.rst

@@ -140,9 +140,6 @@ Python pip                           See the `PyPI package and source code`_ sec
                                         sudo xbps-install streamlink
 ==================================== ===========================================
 
-Please see the `PyPI package and source code`_ or `AppImages`_ sections down below
-if a package is not available for your distro or platform, or if it's out of date.
-
 .. _Arch Linux: https://www.archlinux.org/packages/community/any/streamlink/
 .. _Arch Linux (aur, git): https://aur.archlinux.org/packages/streamlink-git/
 .. _Debian (sid, testing): https://packages.debian.org/unstable/streamlink
@@ -160,6 +157,19 @@ if a package is not available for your distro or platform, or if it's out of dat
 .. _NixOS channel: https://search.nixos.org/packages?show=streamlink&query=streamlink
 
 
+.. note::
+
+    Packaging is not done by the Streamlink maintainers themselves except for
+    the `PyPI package <PyPI package and source code_>`_,
+    the `Windows installers + portable builds <Windows binaries_>`_,
+    and the `Linux AppImages <AppImages_>`_.
+
+    If a package is not available for your operating system / distro or your system's architecture, or if it's out of date
+    or broken, then please contact the respective package maintainers or package-repository maintainers.
+
+    Please open an issue or pull request on GitHub if an available and maintained package is missing.
+
+
 Package maintainers
 -------------------