doc: Rewrite manpage with scdoc

I'm not entirely sure if this is worth it.

On the one hand, I think the source is clearer, easier to read, and
easier to modify.

However, scdoc has a few limitations and odd edge cases, that makes it a
little awkward to work with.

Another alternative is we could use ASCIIDOC with pandoc or asciidoctor
to convert it.

Author: tmccombs

Makefile

@@ -29,7 +29,12 @@ autocomplete/_fd: contrib/completion/_fd
 	$(comp_dir)
 	cp $< $@
 
-install: $(EXE) completions
+doc/fd.1: doc/fd.1.scd
+	scdoc < $< > $@
+
+docs: doc/fd.1
+
+install: $(EXE) completions docs
 	install -Dm755 $(EXE) $(DESTDIR)$(bindir)/fd
 	install -Dm644 autocomplete/fd.bash $(DESTDIR)/$(datadir)/bash-completion/completions/$(exe_name)
 	install -Dm644 autocomplete/fd.fish $(DESTDIR)/$(datadir)/fish/vendor_completions.d/$(exe_name).fish