docs(package): improve subject

- improve format
- add link to mentioned project

subjects/mobile-dev/package/README.md

@@ -1,24 +1,21 @@
 # Package
 
 Package can be used to organize and share a set of functions in Dart. It is simply a sharable library or modules.
-Package is similar to Dart Application except that Dart Package does not have application entry point - main.
+Package is similar to Dart Application except that Dart Package does not have application entry point - `main`.
 A minimal package consists of the following:
 
-- pubspec.yaml:
+- `pubspec.yaml`: a metadata file that declares the package name, version, author, etc.
-  A metadata file that declares the package name, version, author, etc.
+- `lib/`: a directory contains the public code of the package, at least one dart file.
-- lib:
-  The lib directory contains the public code of the package, at least one .dart file.
 
 ### Instructions:
 
-Create a Flutter package for your Secure Notes app. You should write
+Create a Flutter package for your [Secure Notes app](../secure-notes/README.md).
-your own package which will work with sqflite and have CRUD
+You should write your own package which will work with [`sqflite`](https://pub.dev/packages/sqflite) and have CRUD functionality.
-functionality.
+Your package should consist of `Database` class and `Note` class which will allow easy access to SQLite database.
-Your package should consist of Database.dart class and Note class which
+
-will allow easy access to SQLite database.
 In the end you should be able to import it like:
 
-```
+```dart
 import 'package:note/note.dart';
 
 ```
@@ -31,7 +28,7 @@ import 'package:note/note.dart';
 
 ### Database.dart
 
-```
+```dart
 class Database {
 Database _db;
 
@@ -45,26 +42,26 @@ Database _db;
 
 ```
 
-Example of Database class, where you should create table "Note" with 4 parameters :
+Example of Database class, where you should create table `Note` with 4 parameters:
 
-- id
+- `id`
-- title
+- `title`
-- body
+- `body`
-- date
+- `date`
 
-Database class should also have CRUD methods like getAllNotes, deleteAllNotes, addNote, deleteNote, updateNote.
+Database class should also have CRUD methods like `getAllNotes`, `deleteAllNotes`, `addNote`, `deleteNote`, `updateNote`.
 
-- getAllNotes()
+- `getAllNotes()`
-- deleteAllNotes()
+- `deleteAllNotes()`
-- addNote(note: Note)
+- `addNote(note: Note)`
-- deleteNote(note: Note)
+- `deleteNote(note: Note)`
-- updateNote(oldNote: Note, newNote: Note)
+- `updateNote(oldNote: Note, newNote: Note)`
 
 ### Note.dart
 
 Model class for Note object.
 
-```
+```dart
 class Note {
   int id;
   String title;
@@ -80,6 +77,6 @@ class Note {
 
 ```
 
-### Hints:
+### Notions
 
-[https://pub.dev/packages/sqflite](https://pub.dev/packages/sqflite) [https://flutter.dev/docs/development/packages-and-plugins/developing-packages](https://flutter.dev/docs/development/packages-and-plugins/developing-packages)
+[Developing packages with Dart](https://flutter.dev/docs/development/packages-and-plugins/developing-packages)