Update the certificate build directions so that the "fred" certificate would work.

Author: ejohnstown

README.md

@@ -492,9 +492,13 @@ authenticating a user.
 To compile wolfSSH with X.509 support, use the `--enable-certs` build option
 or define `WOLFSSH_CERTS`:
 
-    $ ./configure --enable-certs
+    $ ./configure --enable-certs CPPFLAGS=-DWOLFSSH_NO_FPKI
     $ make
 
+For this example, we are disabling the FPKI checking as the included
+certificate for "fred" does not have the required FPKI extensions. If the
+flag WOLFSSH_NO_FPKI is removed, you can see the certificate get rejected.
+
 To provide a CA root certificate to validate a user's certificate, give the
 echoserver the command line option `-a`.