docs: no justification in home-manager manpage

The `man home-configuration.nix` is configured to left
align the text similar to `man configuration.nix`. This
commit updates the `man home-manager` page to be consitent
with the two manpages mentioned above.

docs/home-manager.1

@@ -1,6 +1,12 @@
 .Dd January 1, 1980
-.Dt home-manager 8
-.Os
+.Dt home-manager 1
+.Os Home Manager
+.\" disable hyphenation
+.nh
+.\" disable justification (adjust text to left margin only)
+.ad l
+.\" enable line breaks after slashes
+.cflags 4 /
 .Sh NAME
 .Nm home-manager
 .Nd reconfigure a user environment