[Documentation] Recipes

[roman-aliyev]

PR adds production-ready solutions for common xcode tasks.

Idea

Each recipe contains complete project.yml and project's file structure. There is also a diff highlighting to highlight the key points that are related to one specific task (unit testing, environments, etc). See this example or other files attached to this PR.

Why?

Xcodegen contains fairly good documentation. But it focuses on xcodegen features and specs. It would be great if the documentation also described solutions to common development tasks with ready-to-use specs.

How to use

By copy-pasting the part or all of project.yml into your app's project.yml file.

Recipe template

# [Name of the recipe]

## Description

[Description]

## File structure

```diff
 .
 ├── Directory
+│   ├── HighlightedFile
 │   └── File.swift
 └── project.yml
```

## project.yml

```diff
 code
+highlighted code
 code
```