Out of date build instructions for wolfSSL support

[0xG0nz0]

Currently the documentation here:

https://libwebsockets.org/lws-api-doc-master/html/md_READMEs_README_8build.html#wolf

states the following:

NOTE: wolfssl needs to be compiled using the --enable-opensslextra flag for this to work.

Per discussion with the wolfSSL team, the correct flag for LWS support is--enable-libwebsockets:

wolfSSL/wolfssl#7432 (comment)

If you just specify --enable-opensslextra you will get lws compile errors when using wolfSSL.