Added add to arglist and set arglist

[joacortez]

• Added the ability to add a visual selection of nodes to the arglist

When using visual selection pressing 'a' will append the current selection to the arglist. Pressing 'A' will overwrite it by emptying the list before appending the selected nodes. This function only adds readable files and ignores directories and non-existant or otherwise undreadable files.

The user will experience:

1. Confirm whether to add node to arglist.

• Update the README file with the new features