message: Update the docs for `tree` to include new format option.
diff: @@ -186,6 +186,10 @@ strings will be replaced with the corresponding value:
  .RS 4
  \h'-04'\(bu\h'+02'\fB{f}\fR \[em] Comma\-separated list of package features that are enabled.
  .RE
  +.sp
  +.RS 4
  +\h'-04'\(bu\h'+02'\fB{lib}\fR \[em] The name of the package's library.
  +.RE
  .RE
  .sp
  \fB\-\-prefix\fR \fIprefix\fR
  