Add cross-doc links, avoid redundancies

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/README.md b/README.md
index ac2a6ab..759ffb5 100644
--- a/README.md
+++ b/README.md
@@ -25,6 +25,8 @@
 1. Run `make apidoc`.
 1. Browse `apidoc/index.html` or `apidoc/modules.html`.
 
+For other sources of documentation, see the [SUPPORT](SUPPORT.md) document.
+
 Compiling
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