Add requirements for the entropy safety switch in documentation.
diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index c42b88d..f800f13 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -286,6 +286,8 @@
* example the MBEDTLS_ENTROPY_HARDWARE_ALT or the MBEDTLS_ENTROPY_NV_SEED
* switch).
*
+ * Requires MBEDTLS_ENTROPY_C, MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES
+ *
* WARNING! This switch is extremely DANGEROUS, don't use it in production code
* under any circumstances. This switch nullifies any security provided by the
* library.
