add errmsg documentation

buffer/errmsg_iam.3

@@ -0,0 +1,19 @@
+.TH errmsg_iam 3
+.SH NAME
+errmsg_iam \- tell errmsg library the name of the program
+.SH SYNTAX
+.B #include <libowfat/errmsg.h>
+
+void \fBerrmsg_iam\fP(const char *\fIprogname\fR);
+.SH DESCRIPTION
+
+Use this function to set the program name.
+
+This function is usually called directly at the start of main() and
+given argv[0] as argument.
+
+This is important for batch processing, so the observer can tell which
+program the error message came from.
+
+.SH "SEE ALSO"
+errmsg(7)