feat coordinate

app/src/main/java/sudoku/Cell.java

@@ -36,4 +36,20 @@ public abstract class Cell {
 			return otherCell.getSymbolIndex() == this.getSymbolIndex();
 		return false;
 	}
+
+	@Override
+	public String toString() {
+		StringBuilder sb = new StringBuilder();
+		sb.append("| ");
+		if (this.symbolIndex != NOSYMBOLE){
+			sb.append(this.symbolIndex);
+		}
+		else {
+			sb.append(" ");
+		}
+
+		sb.append(" |");
+		return sb.toString();
+	}
+
 }