Add more examples

[dcdunkan]

More general examples and plugin (simple and common plugins) examples should be added (In the home page, we can show them separately).

No specific order for now, the more easy to understand the example is, the higher its position.

General

• Hello World
• Echo Bot
• Commands
• Message Formatting
• Filter Queries
• ctx.api and bot.api
• Custom Keyboards
• Inline Keyboards: Alerts, notifications (top of the chat)
• Sessions: Only talk about default memory sessions. Should link to session docs.
• Sending Files: Only about uploading (InputFile, URL, file id).
• Downloading Files
• Simple middlewares: Like logging update events.

Plugins

Only explain basic and commonly used stuff from the plugin. For everything else, must link to their documentation and GitHub repository as additional resources.

• Parse Mode
• i18n
• Conversations
• Emoji
• Menu
• Stateless Question
• Files
• Hydrate