libct: document process.LogLevel field

This field used to hold a string representation of log level (like
"debug" or "info"). Since commit 6c4a3b13d1 this is now a string
holding a numeric representation of log level (e.g. "4"). This was done
in preparation to commit f1b703fc45, and simplifies things in
a few places.

Let's document it.

Fixes: 6c4a3b13d1
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

libcontainer/process.go

@@ -79,6 +79,9 @@ type Process struct {
 
 	ops processOperations
 
+	// LogLevel is a string containing a numeric representation of the current
+	// log level (i.e. "4", but never "info"). It is passed on to runc init as
+	// _LIBCONTAINER_LOGLEVEL environment variable.
 	LogLevel string
 
 	// SubCgroupPaths specifies sub-cgroups to run the process in.