PNaCl documentation: link to ARM 32-bit sandbox internals

native_client_sdk/src/doc/reference/sandbox_internals/index.rst

Index: native_client_sdk/src/doc/reference/sandbox_internals/index.rst
diff --git a/native_client_sdk/src/doc/reference/sandbox_internals/index.rst b/native_client_sdk/src/doc/reference/sandbox_internals/index.rst
index 3b5670d119e7cc7560ab1dc078c5819ddd4a5c6a..3e6e9ed9eee462a2b3d89c5ae681b8d31fc87809 100644
--- a/native_client_sdk/src/doc/reference/sandbox_internals/index.rst
+++ b/native_client_sdk/src/doc/reference/sandbox_internals/index.rst
@@ -9,3 +9,10 @@ Native Client sandboxing, which is also used by Portable Native
 Client. These details can be useful to reimplement a sandbox, or to
 write assembly code that follows sandboxing rules for Native Client
 (Portable Native Client does not allow platform-specific assembly code).
+
+Native Client has sandboxes for:
+
+* :ref:`ARM 32-bit<arm-32-bit-sandbox>`.
+* x86-32
+* x86-64
+* MIPS32