boot: Add Documentation= lines to services

It's a neat way to point folks to the documentation (of course, better
would be to have man pages for each of those services). Also
consistently use Title Case everywhere.

Closes: #1750
Approved by: cgwalters

src/boot/ostree-prepare-root.service

@@ -17,6 +17,7 @@
 
 [Unit]
 Description=OSTree Prepare OS/
+Documentation=man:ostree(1)
 DefaultDependencies=no
 ConditionKernelCommandLine=ostree
 ConditionPathExists=/etc/initrd-release