add openssl-conference.org banner to home page (#7)

Author: quarckster

scaffold/images/openssl-conference-banner.jpg

@@ -15,3 +15,5 @@ migrating existing applications to OpenSSL 3.0 are available in the
 
 Information related to the OpenSSL FIPS Validation [FIPS 140-2 validation](fips.md) is also
 available.
+
+[![OpenSSL Conference 2025](images/openssl-conference-banner.jpg "OpenSSL Conference 2025")](https://openssl-conference.org)