Don't use the PSA specification as Mbed TLS documentation

The Doxygen-generated manual includes PSA interfaces, so we don't need
to tell people to read the specification instead. Do link to the
specification portal, but from the PSA API section, not from the Mbed
TLS documentation section.
diff --git a/README.md b/README.md
index 375f9ae..de1dd27 100644
--- a/README.md
+++ b/README.md
@@ -25,8 +25,6 @@
 1. Run `make apidoc`.
 1. Browse `apidoc/index.html` or `apidoc/modules.html`.
 
-For the PSA cryptography interfaces, please refer to the PSA Cryptography API documents linked from the [PSA cryptography interfaces documentation portal](https://armmbed.github.io/mbed-crypto/psa/#application-programming-interface) for an overview of the library's interfaces and a detailed description of the types, macros and functions that it provides. The API reference is available in [PDF](https://armmbed.github.io/mbed-crypto/PSA_Cryptography_API_Specification.pdf) and [HTML](https://armmbed.github.io/mbed-crypto/html/index.html) formats.
-
 Compiling
 ---------
 
@@ -216,6 +214,10 @@
 
 Arm welcomes feedback on the design of the API. If you think something could be improved, please open an issue on our Github repository. Alternatively, if you prefer to provide your feedback privately, please email us at [`mbed-crypto@arm.com`](mailto:mbed-crypto@arm.com). All feedback received by email is treated confidentially.
 
+### PSA API documentation
+
+A browsable copy of the PSA Cryptography API documents is available on the [PSA cryptography interfaces documentation portal](https://armmbed.github.io/mbed-crypto/psa/#application-programming-interface) in [PDF](https://armmbed.github.io/mbed-crypto/PSA_Cryptography_API_Specification.pdf) and [HTML](https://armmbed.github.io/mbed-crypto/html/index.html) formats.
+
 ### PSA implementation in Mbed TLS
 
 Mbed TLS includes a reference implementation of the PSA Cryptography API.