Document the history of BIO_gets() on BIO_fd().

Reviewed-by: NRich Salz <rsalz@openssl.org>
Reviewed-by: NRichard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3442)

doc/man3/BIO_read.pod

@@ -80,6 +80,11 @@ to the chain.
 
 L<BIO_should_retry(3)>
 
+=head1 HISTORY
+
+BIO_gets() on 1.1.0 and older when called on BIO_fd() based BIO does not
+keep the '\n' at the end of the line in the buffer.
+
 =head1 COPYRIGHT
 
 Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.