Add `RUBY_BUGREPORT_PATH` to the manual page

man/ruby.1

@@ -645,6 +645,39 @@ Machine stack size used at fiber creation.
 default: 262144 or 524288
 .Pp
 .El
+.Sh BUG REPORT ENVIRONMENT
+.Pp
+.Bl -tag -compact -width "RUBY_BUGREPORT_PATH"
+.It Ev RUBY_BUGREPORT_PATH
+The template of path name to save bug report.
+default: none
+.El
+.Ss Naming bug report files
+The template can contain % specifiers which are substituted
+by the following values when a bug report file is created:
+.Pp
+.Bl -hang -compact -width "%NNN"
+.It %%
+A single % character.
+.It %e
+Basename of executable.
+.It %E
+Pathname of executable,
+with slashes (\fB/\fP) replaced by exclamation marks (\fB!\fP).
+.It %p
+PID of dumped process.
+.It %t
+Time of dump, expressed as seconds since the
+Epoch, 1970-01-01 00:00:00 +0000 (UTC).
+.El
+.Pp
+A single % at the end of the template is dropped from the
+core filename, as is the combination of a % followed by any
+character other than those listed above.
+All other characters in the template become a literal
+part of the core filename.
+The template may include \(aq/\(aq characters, which are interpreted
+as delimiters for directory names.
 .Sh SEE ALSO
 .Bl -hang -compact -width "https://www.ruby-toolbox.com/"
 .It Lk https://www.ruby-lang.org/