Handbook: Add a small chapter about doas as an alternative to sudo

doas is a viable alternative to sudo, so it is worth to be
mentioned in our handbook.

Reviewed by:	0mp (early version)
Differential Revision:	https://reviews.freebsd.org/D28483

documentation/content/en/books/handbook/security/_index.adoc

@@ -2125,3 +2125,26 @@ While sessions are logged, any administrator is able to remove sessions and leav
 ====
 
 The `sudoreplay` is extremely extendable. Consult the documentation for more information.
+
+[[security-doas]]
+As an alternative to package:security/sudo[] package:security/doas[] can be used to provide the ability for users to get enhanced privileges.
+
+The doas utility is available via the ports collection in package:security/doas[] or via the man:pkg[8] utility.
+
+After the installation [.filename]#/usr/local/etc/doas.conf# must be configured to grant access for users for specific commands, or roles.
+
+The simpliest entry could be the following, which grants local_user root permissions without asking for its password when executing the doas command.
+
+[source,bash]
+....
+permit nopass local_user as root
+....
+
+For more configuration examples, please read man:doas.conf[5].
+
+After the installation and configuration of the `doas` utility, a command can now be executed with enhanced privileges, like for example.
+
+[source,bash]
+....
+$ doas vi /etc/rc.conf
+....