Create landing pages for PSA Crypto and for each driver type
There isn't much content yet, we'll populate it over time as the
interface stabilizes and as more material becomes available.
diff --git a/docs/psa/entropy/index.md b/docs/psa/entropy/index.md
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+# PSA entropy source driver interface
+
+The accelerator interface lets you drivers for entropy sources such as Hardware Random Number Generators (HRNG), also known as True Random Number Generators (TRNG), into an implementation of the [PSA Cryptography API](../#application-programming-interface).
+
+**Status: draft** — major changes are still likely.
+
+**Documentation**: for now, please see the header file:
+[`include/psa/crypto_entropy_driver.h`](https://github.com/ARMmbed/mbed-crypto/blob/development/include/psa/crypto_entropy_driver.h)