Add missing .. availability::s

Author: StanFromIreland

Doc/library/curses.rst

@@ -24,6 +24,8 @@ Linux and the BSD variants of Unix.
 
 .. include:: ../includes/optional-module.rst
 
+.. availability:: Unix.
+
 .. note::
 
    Whenever the documentation mentions a *character* it can be specified

Doc/library/dbm.rst

@@ -240,6 +240,8 @@ functionality like crash tolerance.
 
 .. include:: ../includes/wasm-mobile-notavail.rst
 
+.. availability:: Unix.
+
 .. exception:: error
 
    Raised on :mod:`!dbm.gnu`-specific errors, such as I/O errors. :exc:`KeyError` is
@@ -370,6 +372,8 @@ This module can be used with the "classic" NDBM interface or the
 
 .. include:: ../includes/wasm-mobile-notavail.rst
 
+.. availability:: Unix.
+
 .. exception:: error
 
    Raised on :mod:`!dbm.ndbm`-specific errors, such as I/O errors. :exc:`KeyError` is raised

Doc/library/readline.rst

@@ -27,6 +27,8 @@ Readline library in general.
 
 .. include:: ../includes/optional-module.rst
 
+.. availability:: Unix.
+
 .. note::
 
   The underlying Readline library API may be implemented by