[Doc] Documents the new option -explain.

doc/userman/user-services.tex

@@ -89,7 +89,7 @@ loading another project file.
 Options \optionuse{-}{help}, \optionuse{-}{verbose},
 \optionuse{-}{debug}\xspace(and 
 their corresponding plugin-specific counterpart) 
-as well as \optionuse{-}{quiet}\xspace and
+as well as \optionuse{-}{explain}, \optionuse{-}{quiet}\xspace and
 \optionuse{-}{unicode}\xspace are not saved on disk.
 
 \section{Dependencies between Analyses}
@@ -185,5 +185,5 @@ generates (resp. does not generate) a journal upon exiting the session.
 
 Modifications of options \optionuse{-}{help}, \optionuse{-}{verbose},
 \optionuse{-}{debug}\xspace (and their corresponding counterpart) as well as
-\optionuse{-}{quiet}\xspace and \optionuse{-}{unicode}\xspace are not written in
-the journal.
+\optionuse{-}{explain}, \optionuse{-}{quiet}\xspace and
+\optionuse{-}{unicode}\xspace are not written in the journal.

doc/userman/user-start.tex

@@ -132,6 +132,10 @@ while \optiondef{-}{version} prints the \FramaC version only
 The options of the installed plug-ins are displayed by using either the
 option \texttt{-<plug-in shortname>-help} or \texttt{-<plug-in shortname>-h}.
 
+Finally, the option \optiondef{-}{explain} can be used to obtain information
+about some specific options of the kernel or of any installed plug-ins:
+it prints a help message for each other option given in the command line.
+
 \subsection{\FramaC Configuration}\label{sec:version}
 
 The complete configuration of \FramaC can be obtained with various options,

man/frama-c.1.md

@@ -55,6 +55,9 @@ option which has the opposite effect.
 -kernel-help
 : prints the list of options recognized by Frama-C's kernel
 
+-explain
+: prints a help message for each other option given in the command line
+
 -verbose *n*
 : sets verbosity level. Defaults to 1.
 Setting it to 0 will output less progress messages.