9pfid(2): document struct Qid (thanks sirjofri)

The Qid struct is pervasive when writing 9p servers,
but is not described in the manpages. This adds a
definition to the 9pfid manpage.

sys/man/2/9pfid

@@ -14,6 +14,17 @@ Req, Reqpool, allocreqpool, freereqpool, allocreq, closereq, lookupreq, removere
 .PP
 .ft L
 .nf
+.ta \w'\fL    'u +\w'\fLuvlong 'u
+typedef struct Qid
+{
+	uvlong	path;
+	ulong	vers;
+	uchar	type;
+} Qid;
+.fi
+.PP
+.ft L
+.nf
 .ta \w'\fL    'u +\w'\fLulong 'u
 typedef struct Fid
 {