Docs: Initial documentation structure using Sphinx

[pedrominatel]

This PR is the initial documentation structure including the basic information about the project and Sphinx configuration.

CONTENTS:

• Getting Started
• Installing
• Boards
• Libraries
• Library Builder
• Tutorials
• ESP-IDF as Component
• OTA Web Update
• makeEspArduino
• Troubleshooting
• Contributing

This PR also changes the README.md.

[pedrominatel]

PTAL @me-no-dev and let me know if any other change is required.

[VojtechBartoska]

Few notes and content Table fix of Readme.md file.

[wujiangang]

Can we move Installing and Boards sections under Getting Started? Add a section named such as Advanced Utilities, and move Library Builder, ESP-IDF as Component, OTA Web Update, makeEspArduino inside. So the CONTENTS will be concise.

[pedrominatel]

Can we move Installing and Boards sections under Getting Started? Add a section named such as Advanced Utilities, and move Library Builder, ESP-IDF as Component, OTA Web Update, makeEspArduino inside. So the CONTENTS will be concise.

I just think we should keep Library Builder and ESP-IDF as Component as is because both are often used. We can move them to Advanced Utilities when the content index gets bigger.