docs: add links to dependencies

Author: Ginden

content/techniques/caching.md

@@ -4,7 +4,7 @@ Caching is a great and simple **technique** that helps improve your app's perfor
 
 #### Installation
 
-First install required packages:
+First install [required packages](https://github.com/BryanDonovan/node-cache-manager) (and its types for TypeScript users):
 
 ```bash
 $ npm install cache-manager

content/techniques/cookies.md

@@ -4,7 +4,7 @@ An **HTTP cookie** is a small piece of data stored by the user's browser. Cookie
 
 #### Use with Express (default)
 
-First install the required package (and its types for TypeScript users):
+First install the [required package](https://github.com/expressjs/cookie-parser) (and its types for TypeScript users):
 
 ```shell
 $ npm i cookie-parser

content/techniques/mongo.md

@@ -2,7 +2,7 @@
 
 Nest supports two methods for integrating with the [MongoDB](https://www.mongodb.com/) database. You can either use the built-in [TypeORM](https://github.com/typeorm/typeorm) module described [here](/techniques/database), which has a connector for MongoDB, or use [Mongoose](https://mongoosejs.com), the most popular MongoDB object modeling tool. In this chapter we'll describe the latter, using the dedicated `@nestjs/mongoose` package.
 
-Start by installing the required dependencies:
+Start by installing the [required dependencies](https://github.com/Automattic/mongoose):
 
 ```bash
 $ npm install --save @nestjs/mongoose mongoose

content/techniques/sessions.md

@@ -4,7 +4,7 @@
 
 #### Use with Express (default)
 
-First install the required package (and its types for TypeScript users):
+First install the [required package](https://github.com/expressjs/session) (and its types for TypeScript users):
 
 ```shell
 $ npm i express-session

content/techniques/validation.md

@@ -24,7 +24,7 @@ $ npm i --save class-validator class-transformer
 
 > info **Hint** The `ValidationPipe` is exported from the `@nestjs/common` package.
 
-Because this pipe uses the `class-validator` and `class-transformer` libraries, there are many options available. You configure these settings via a configuration object passed to the pipe. Following are the built-in options:
+Because this pipe uses the [`class-validator`](https://github.com/typestack/class-validator) and [`class-transformer`](https://github.com/typestack/class-transformer) libraries, there are many options available. You configure these settings via a configuration object passed to the pipe. Following are the built-in options:
 
 ```typescript
 export interface ValidationPipeOptions extends ValidatorOptions {