sslkeylogfile.md: LibreSSL does not support this:

Ref: curl/curl#13672

usingcurl/tls/sslkeylogfile.md

@@ -25,6 +25,8 @@ Support for `SSLKEYLOGFILE` is provided by libcurl itself - making it possible f
 
 The support for `SSLKEYLOGFILE` requires that curl was built with a TLS
 backend that supports this feature. The backends that support SSLKEYLOGFILE
-are: OpenSSL, libressl, BoringSSL, GnuTLS and wolfSSL.
+are: OpenSSL, AWS-LC, BoringSSL, GnuTLS and wolfSSL. (Note that this list does
+not include LibreSSL in spite of it being an OpenSSL fork.)
 
-If curl was built to use another backend, you cannot record your curl TLS traffic this way.
+If curl was built to use another backend, you cannot record your curl TLS
+traffic this way.