added PLT documentation structure to Community section

[TinaKT]

Purpose

Adds PLT documentation in a separate branch that can be merged when desired.
Documentation is based on information in Google doc DevNet Tutorial and tutorials on Discord.

The documentation will be located under "Community" and is organized in the following structure:

Protocol Layer Tokens (PLTs) (top section)

Get started with PLT DevNet

• Set up Browser Wallet for DevNet
• Connect to DevNet
• Create a DevNet identity
• Create a DevNet account
• Request test CCD
• Request PLT issuance

PLT operations

• Create and manage PLTs
• Transfer PLTs
• Query PLT information

PLT integration

• Using Concordium Client with PLTs
• Web SDK integration
• Rust SDK integration

Checklist

• My code follows the style of this project.
• The code compiles without warnings.
• I have performed a self-review of the changes.
• I have documented my code, in particular the intent of the
  hard-to-understand areas.

By submitting the contribution I accept the terms and conditions of the
Contributor License Agreement v1.0

• link: https://developers.concordium.com/CLAs/Contributor-License-Agreement-v1.0.pdf

[bogacyigitbasi]

Mostly simple updates, it is great to have the docs on PLTs available! if you feel like my comment is not relevant let me know.