Add documentation/usage for --coverimage.

doc/mxmldoc.man

@@ -11,7 +11,7 @@
 .\"
 .\"     https://michaelrsweet.github.io/mxml
 .\"
-.TH mxmldoc 1 "Mini-XML" "11 April 2017" "Michael R Sweet"
+.TH mxmldoc 1 "Mini-XML" "30 April 2017" "Michael R Sweet"
 .SH NAME
 mxmldoc \- mini-xml documentation generator
 .SH SYNOPSIS
@@ -138,6 +138,8 @@ mxmldoc \- mini-xml documentation generator
 .I bodyfile
 ] [ \-\-copyright
 .I copyright
+] [ \-\-coverimage
+.I image.png
 ] [ \-\-docversion
 .I version
 ] [ \-\-feedname

mxmldoc.c

@@ -3587,6 +3587,7 @@ usage(const char *option)		/* I - Unknown option */
   puts("    --author name              Set author name");
   puts("    --body bodyfile            Set body file (markdown supported)");
   puts("    --copyright text           Set copyright text");
+  puts("    --coverimage image.png     Set cover image (EPUB)");
   puts("    --css filename.css         Set CSS stylesheet file");
   puts("    --docset bundleid.docset   Generate documentation set");
   puts("    --docversion version       Set documentation version");