Improve command suggestion for installing statistics package from Octave Forge

The “io” package is a dependency, hence must be explicitly installed first.

[skip ci]

matlab/dynare_config.m

@@ -102,7 +102,7 @@ if isoctave
     % Our replacement functions don't work under Octave (because of gamrnd, see
     % #1638), hence the statistics toolbox is now a hard requirement
     if ~user_has_octave_forge_package('statistics')
-        error('You must install the "statistics" package from Octave Forge, either with your distribution package manager or with "pkg install -forge statistics"')
+        error('You must install the "statistics" package from Octave Forge, either with your distribution package manager or with "pkg install -forge io statistics"')
     end
 else
     if ~user_has_matlab_license('statistics_toolbox')