doc/toolbox: Restore --verbose

It's good to document the --log-level and --log-podman flags because
they can give us some flexibility with the logging in future, but it's
still desirable to keep --verbose (and the -vv trick) in the manual.

Toolbox is still a small enough code base that not too many log levels
are actually needed, yet. The complexity of remembering which log
level reveals which detail soon starts to outweigh the simplicity of
dumping as much as possible, since there aren't that many log messages
to begin with. It's a lot easier to type and remember things like
--verbose, -v and -vv, than their newer counterparts, and they are a
reasonably widely used convention (eg., flatpak, nmap, ssh, etc.).

If some day Toolbox grows to have a significantly larger number of log
messages, then it's possible that --verbose would be of less use, but
that's not the case today.

https://github.com/containers/toolbox/pull/814

doc/toolbox.1.md

@@ -8,6 +8,7 @@ toolbox - Tool for containerized command line environments on Linux
         [*--help* | *-h*]
         [*--log-level LEVEL*]
         [*--log-podman*]
+        [*--verbose* | *-v*]
         *COMMAND* [*ARGS*...]
 
 ## DESCRIPTION
@@ -60,6 +61,10 @@ Log messages above specified level: debug, info, warn, error, fatal or panic
 Show log messages of invocations of Podman based on the logging level specified
 by option **log-level**.
 
+**--verbose, -v**
+
+Same as `--log-level=debug`. Use `-vv` to include `--log-podman`.
+
 ## COMMANDS
 
 Commands for working with toolbox containers and images: