Note a workaround for missing system libmpdec-dev when building (#1371)

Author: hughsw

getting-started/setup-building.rst

@@ -660,6 +660,8 @@ on Linux, macOS and iOS.
             libncurses5-dev libreadline6-dev libsqlite3-dev libssl-dev \
             lzma lzma-dev tk-dev uuid-dev zlib1g-dev libmpdec-dev
 
+   Note that Debian 12 and Ubuntu 24.04 do not have the ``libmpdec-dev`` package.  You can safely
+   remove it from the install list above and the Python build will use a bundled version.
 
 .. tab:: macOS