libssh2_knownhost_readfile.3: clarify return value

This function returns the number of parsed hosts on success, not just
zero as previously documented.

docs/libssh2_knownhost_readfile.3

@@ -1,5 +1,5 @@
 .\"
-.\" Copyright (c) 2009 by Daniel Stenberg
+.\" Copyright (c) 2009-2011 by Daniel Stenberg
 .\"
 .TH libssh2_knownhost_readfile 3 "28 May 2009" "libssh2 1.2" "libssh2 manual"
 .SH NAME
@@ -19,8 +19,8 @@ collection of known hosts.
 \fILIBSSH2_KNOWNHOST_FILE_OPENSSH\fP is the only currently supported
 format. This file is normally found named ~/.ssh/known_hosts
 .SH RETURN VALUE
-Returns a regular libssh2 error code, where negative values are error codes
-and 0 indicates success.
+Returns a negative value, a regular libssh2 error code for errors, or a
+positive number as number of parsed known hosts in the file.
 .SH AVAILABILITY
 Added in libssh2 1.2
 .SH SEE ALSO