Empty docstring causes a bounds error

[tecosaur]

If a blank command description is given, a bounds error is thrown.

using Comonicon
"""
"""
@main

This is caused by

Comonicon.jl/src/frontend/markdown.jl

Lines 134 to 140 in ebb1833

	function read_content(md::Markdown.MD)
	if md.content[1] isa Markdown.MD
	return read_content(md.content[1])
	else
	return md.content
	end
	end

Where we see [1] before checking that there is any content at all.

Comonicon 0.12.17/master