docs: extend home-configuration.nix header

The previous version had a longer header before the options,
including a DESCRIPTION section and an header for the OPTIONS.

docs/home-configuration-nix-header.5

@@ -7,3 +7,11 @@
 .cflags 4 /
 .SH "NAME"
 \fIhome\-configuration\&.nix\fP \- Home Manager configuration specification
+.SH "DESCRIPTION"
+.sp
+The file ~/\&.config/home\-manager/home\&.nix contains the declarative specification of your Home Manager configuration\&. The command \fBhome\-manager\fR takes this file and realises the user environment configuration specified therein\&.
+.SH "OPTIONS"
+.PP
+You can use the following options in
+home\-configuration\&.nix:
+.PP