Is there a script to add the description as an editable panel alongside of name, keywords, etc?

Here is a more fleshed-out script. Right-click your file(s) and select "Edit Description." The script reads dc:description from the first file, displays it in a window, and lets you edit and apply the changes to all selected files.

#target bridge
if(BridgeTalk.appName == 'bridge'){
    var descCmd = MenuElement.create('command', 'Edit Description...', 'after Thumbnail/Open', this.menuID); //add to Contextual menu
    }

descCmd.onSelect = function(){
    descMain();
    }

descMain = function(){
    try{
        var descThumbs = app.document.selections; //get selected thumbnails
        if(!descThumbs.length) return; //nothing selected
        var descr = '';
        if(!descThumbs[0].hasMetadata) return; //no metadata
        var descMeta = descThumbs[0].synchronousMetadata;
        var descXMP = new XMPMeta(descMeta.serialize());
        if(descXMP.doesPropertyExist(XMPConst.NS_DC, 'description')){
            descr = descMeta.read(XMPConst.NS_DC, 'description');
            descr = descr.toString();
            }
        else{
            descr = '';
            }
        descWindow = new Window ('palette', 'Edit Description', undefined);
        descPanel = descWindow.add('panel', undefined, '');
        descPanel.orientation = 'column';
        descPanel.alignChildren = ['left', 'top'];
        descPanel.lbl1 = descPanel.add('statictext', undefined, 'Description:');
        descPanel.lbl1.graphics.font = 'palette-bold';
        descPanel.txt1 = descPanel.add('edittext {justify:"left"}', undefined, '');
        descPanel.txt1.preferredSize = [350, 80];
        descPanel.txt1.text = descr;
        descPanel.grp1 = descPanel.add('group', undefined, '');
        descPanel.grp1.preferredSize = [350, 50];
        descPanel.grp1.orientation = 'row';
        descPanel.grp1.alignment = ['fill', 'fill'];
        descPanel.grp1.margins = [30, 20, 0, 0];
        descPanel.grp1.button1 = descPanel.grp1.add('button', undefined, 'Cancel', {name: 'cancel'});
        descPanel.grp1.button2 = descPanel.grp1.add('button', undefined, 'Apply Changes', {name: 'ok'});
        descPanel.grp1.button2.enabled = false;

        descPanel.txt1.onChanging = function(){
            descPanel.grp1.button2.enabled = true;
            }

        descPanel.grp1.button1.onClick = function(){
            descWindow.close();
            }

        descPanel.grp1.button2.onClick = function(){
            descr = descPanel.txt1.text;
            descWindow.close();
            for(var a in descThumbs){ //loop through thumbs
                if(!descThumbs[a].container){
                    try{
                        descMeta = descThumbs[a].synchronousMetadata;
                        descXMP = new XMPMeta(descMeta.serialize());
                        descXMP.deleteProperty(XMPConst.NS_DC, 'description');
                        descXMP.setLocalizedText(XMPConst.NS_DC, 'description', null, 'x-default', descr);
                        var descUpdatedPacket = descXMP.serialize(XMPConst.SERIALIZE_OMIT_PACKET_WRAPPER | XMPConst.SERIALIZE_USE_COMPACT_FORMAT);
                        descThumbs[a].metadata = new Metadata(descUpdatedPacket); //write to file
                        }
                    catch(e){
                        Window.alert(e + e.line);
                        }
                    }
                }
            }
        descWindow.layout.layout(true);
        descWindow.show();
        descPanel.txt1.active = true;
        }
    catch(e){
        Window.alert(e + e.line);
        }
    }

You can't add to the built-in panels.

You might be able to use the Custom Metadata Panel found here:

https://github.com/adobe-dmeservices/custom-metadata

Below is a sample script for writing text to the dc:description field.

#target bridge
if(BridgeTalk.appName == 'bridge'){
    var descltCmd = MenuElement.create('command', 'Edit Description...', 'after Thumbnail/Open', this.menuID); //add to Contextual menu
    }
descltCmd.onSelect = function(){
    descltMain();
    }

descltMain = function(){
    var descThumbs = app.document.selections; //get selected thumbnails
    if(!descThumbs.length) return; //nothing selected
    var descr = '';
    descr = Window.prompt('Enter new description');
    if(descr == null){
        return;
        }
    for(var a in descThumbs){ //loop through thumbs
        if(!descThumbs[a].container){
            try{
                var descMeta = descThumbs[a].synchronousMetadata;
                var descXMP = new XMPMeta(descMeta.serialize());
                descXMP.deleteProperty(XMPConst.NS_DC, 'description');
                descXMP.setLocalizedText(XMPConst.NS_DC, 'description', null, 'x-default', descr);
                var descUpdatedPacket = descXMP.serialize(XMPConst.SERIALIZE_OMIT_PACKET_WRAPPER | XMPConst.SERIALIZE_USE_COMPACT_FORMAT);
                descThumbs[a].metadata = new Metadata(descUpdatedPacket); //write to file
                }
            catch(e){
                alert(e + e.line);
                }
            }
        }
    }