description tag should be added in auto-completion

[FaizanFrolic]

It will be good if we add a "description" tag as well in auto-completion option

i.e. for example in case of leaf

leaf leaf-name {
            type type-name {
                
            }
}

to

leaf leaf-name {
            description "TODO: add description";
            type type-name {
                
            }
        }

[dhuebner]

@FaizanFrolic
That would be easy to add I think.

This is also related: #212