[contextualprocess] Document corner-case

The "*" will match its literal value, but is also used as a wildcard.

src/modules/contextualprocess/contextualprocess.conf

@@ -17,7 +17,10 @@
 #
 # As a special case, the value-check "*" matches any value, but **only**
 # if no other value-check matches. Use it as an *else* form for value-
-# checks. Take care to put the asterisk in quotes.
+# checks. Take care to put the asterisk in quotes. The value-check "*"
+# **also** matches a literal asterisk as value; a confusing corner case
+# is checking for an asterisk **and** having a wildcard match with
+# different commands. This is currently not possible.
 #
 # Global configuration variables are not checked in a deterministic
 # order, so do not rely on commands from one variable-check to