Description of problem:

There is no "Documentation=" line in "[Unit]" section of the
/usr/lib/systemd/service/httpd.service that references the man pages or
documentation files. Same for htcacheclean.service.

That's why "systemctl status httpd.service" doesn't show the "Docs:"
section and "systemctl help httpd.service" doesn't open the man pages.

Version-Release number of selected component (if applicable):

httpd-2.4.6-19.el7

How reproducible:

Query the httpd.service.

Steps to Reproduce:
1. systemctl status httpd.service
2. systemctl help httpd.service
3.

Actual results:

"systemctl status httpd.service" doesn't show a "Docs:" section

"systemctl help httpd.service" prints "Documentation for httpd.service not known." 


Expected results:

"systemctl status httpd.service" should show a "Docs:" section:

# systemctl status httpd.service
httpd.service - The Apache HTTP Server
   Loaded: loaded (/etc/systemd/system/httpd.service; enabled)
   Active: active (running) since Tue 2015-01-20 17:16:48 CET; 4min 14s ago
     Docs: man:httpd(8)
           man:apachectl(8)
 Main PID: 7657 (httpd)
   Status: "Total requests: 0; Current requests/sec: 0; Current traffic:   0 B/sec"
   CGroup: /system.slice/httpd.service
[...]

"systemctl help httpd.service" should open the man pages.

Additional info:

The Documentation= line in httpd.service could look like this:

# grep ^Documentation= httpd.service 
Documentation=man:httpd(8)
Documentation=man:apachectl(8)

The same applies to /usr/lib/systemd/service/htcacheclean.service:

# grep ^Documentation= htcacheclean.service 
Documentation=man:htcacheclean(8)

There are some other systemd unit files without a "Documentation=" line.
You should really consider a generic unit file check for the entire distribution.

Also, a systemd-lint utility would be awesome.