Add icon for Pico (Plenti template engine)

[jimafisk]

Requirements

• I have searched the (also closed) issues for the icon and found nothing related or helpful
• I have searched the suggestion list

Justification

The Plenti SSG (https://github.com/plentico/plenti) formerly used Svelte templates, but has a new templating engine called Pico (https://github.com/plentico/pico). I'm hoping to add support so Neovim users don't lose file extension support in their editors.

I have created a PR for it's addition here: #1985

Description

The icon for Pico templates should be the project's logo: https://github.com/plentico

Use scenario

Neovim users often rely on visual file extensions to more easily scan a codebase file structure (a typical combo is nvim-tree + nvim-web-devicons). This addition would allow .pico file support in Plenti projects.

Icon license

MIT