Adding documentation to CheckRunFileList macro

[jgalan]

Just adding documentation to CheckRunFileList macro.

This macro can be used to identify files that were not properly closed, e.g.: after launching the processing to condor cluster.

restManager CheckRunFileList "/path/file*Pattern.root"

The documentation will be printed when using REST_PrintMacros.C.

[jgalan]

Any ideas to improve the macro are welcome. I thought perhaps it might be interesting to return the list of filenames that cannot be open properly in a std::vector <std::string>, instead of just printing on screen.