update 'Core Modules' description

Author: sommersoft

shared-bindings/index.rst

@@ -1,11 +1,11 @@
 Core Modules
 ========================================
 
-These core modules are intended on being consistent across ports. Currently
-they are only implemented in the SAMD21 and ESP8266 ports. A module may not exist
-in a port if no underlying hardware support is present or if flash space is
-limited. For example, a microcontroller without analog features will not have
-`analogio`.
+These core modules are intended on being consistent across ports and boards.
+A module may not exist on a port/board if no underlying hardware support is
+present or if flash space is limited. For example, a microcontroller without
+analog features will not have `analogio`. See the `support_matrix` page for
+a list of modules supported on each board.
 
 Modules
 ---------