docs: update docs

Signed-off-by: Luca Di Maio <luca.dimaio1@gmail.com>

distrobox-host-exec

@@ -55,7 +55,7 @@ Options:
 	--version/-V:		show version
     --yes/-Y:      Automatically answer yes to prompt:
                                 host-spawn will be installed on the guest system
-                                if host-spawn is detected.
+                                if host-spawn is not detected.
                                 This behaviour is default when running in a non-interactive shell.
 EOF
 }
@@ -129,7 +129,7 @@ if  ! command -v host-spawn > /dev/null ||
 	# if non-interactive flag flag hasn't been set
 	if [ "${non_interactive}" -eq 0 ]; then
 		# Prompt to download it.
-		printf "Distrobox Warning: no host-spawn found!\n"
+		printf "Warning: host-spawn not found or version is too old!\n"
 		printf "Do you want to install host-spawn utility? [Y/n] "
 		read -r response
 		response=${response:-"Y"}

docs/usage/distrobox-host-exec.md

@@ -7,9 +7,9 @@
 
 distrobox-host-exec lets one execute command on the host, while inside of a container.
 
-If "flatpak-spawn" is installed in the container, this is what is used, and it is the
-most powerful and recommended method. If, instead, "flatpak-spawn" can't be found, it
-still try to get the job done with "host-spawn", an alternative project.
+Under the hood, distrobox-host-exec uses `host-spawn` a project that let's us
+execute commands back on the host.
+If the tool is not found the user will be prompted to install it.
 
 # SYNOPSIS