Added WelcomePanel, containing helpful startup text

src/main/java/cz/muni/fi/pv168/project/ui/main/panel/WelcomePanel.java

+package cz.muni.fi.pv168.project.ui.main.panel;
+
+import javax.swing.BorderFactory;
+import javax.swing.JPanel;
+import javax.swing.JTextArea;
+import javax.swing.border.EmptyBorder;
+import javax.swing.border.EtchedBorder;
+import java.awt.BorderLayout;
+import java.awt.Color;
+import java.awt.Font;
+
+public class WelcomePanel {
+
+    private final JPanel panel;
+    private static final String WELCOME_MESSAGE =
+            "Welcome to to:do, your daily task reminder.\n" + "\n" +
+            "You can use the toolbar buttons above to add, edit, or delete tasks and categories.\n" +
+            "Switch between tasks and categories using the tabs.\n" +
+            "Click on a task in the list on the left to see details.";
+
+    public WelcomePanel() {
+        var welcomeTextArea = new JTextArea(WELCOME_MESSAGE);
+        welcomeTextArea.setFont(new Font(Font.SANS_SERIF, welcomeTextArea.getFont().getStyle(), 20));
+        welcomeTextArea.setLineWrap(true);
+        welcomeTextArea.setWrapStyleWord(true);
+        welcomeTextArea.setEditable(false);
+
+        panel = new JPanel(new BorderLayout());
+        panel.setBorder(BorderFactory.createCompoundBorder(new EtchedBorder(EtchedBorder.LOWERED), new EmptyBorder(50, 50, 50, 50)));
+        welcomeTextArea.setBackground(new Color(panel.getBackground().getRGB()));
+        panel.add(welcomeTextArea);
+    }
+
+    public JPanel getPanel() {
+        return panel;
+    }
+}