Remove user, add dryRun

* Remove user option, shoud be defined in config or SSH will use default
* Improve usage()
* Add dryRun option
* Some syntax enhancement

README.md

@@ -1,13 +1,28 @@
-# csc : cluster ssh command
+# csc : Cluster SSH Command
 
-simple script to execute command over ssh on remote hosts with "dialog" DEBIAN_FRONTEND
+Launch command over SSH on cluster hosts with "dialog" DEBIAN_FRONTEND.
+
+## Tree
+
+```bash
+$ tree
+.
+├── csc
+└── README.md
+
+0 directories, 2 files
+```
 
 ## Usage
 
+```bash
+$ csc -h
 Usage: csc [OPTION]... [COMMAND]
-    -v  enable verbose mode
-    -c  specify config dir, default is /$HOME/.config/csc
-    -u  specify user, default is $USER
-    -g  specify hosts group
-    
-Host group file must exists under config dir, one host per line
+  -h  show help
+  -v  enable verbose mode
+  -c  specify config dir, default is /home/flo/.config/csc
+  -g  specify group
+  -d  enable dry run mode
+```
+
+Host group file must exists under config dir, one host per line.