Improve our documentation for the NT Service command line options

We explain the --options option, document --nt-service as an
internal-use-only thing (which it is), fix a URL, and generally
improve the prose.

changes/bug3964

+  o Documentation fixes:
+    - Improve the manual's documentation for the NT Service command-line
+      options. Addresses bug 3964.
+

doc/tor.1.txt

@@ -45,10 +45,16 @@ OPTIONS
 **--verify-config**::
     Verify the configuration file is valid.
 
+**--service install** [**--options** __command-line options__]::
+    Install an instance of Tor as a Windows service, with the provided
+    command-line options. Current instructions can be found at
+    https://trac.torproject.org/projects/tor/wiki/doc/TorFAQ#HowdoIrunmyTorrelayasanNTservice
+
+**--service** **remove**|**start**|**stop**::
+    Remove, start, or stop a configured Tor Windows service.
+
 **--nt-service**::
-    **--service [install|remove|start|stop]** Manage the Tor Windows
-    NT/2000/XP service. Current instructions can be found at
-    https://wiki.torproject.org/noreply/TheOnionRouter/TorFAQ#WinNTService
+    Used internally to implement a Windows service.
 
 **--list-torrc-options**::
     List all valid options.