Add 2 new plugins to README (symbol and recent-files)

[ffpyt]

Add two new Python plugins: Recent Files & Unicode Symbols

This PR adds two new Python plugins for Albert.

🕓 Recent Files

Provides quick access to recently used files and folders via GTK's RecentManager. Features include:

• Filter modifiers to narrow results by type — directories (d), videos (v), audio (a), images (i), or files only (f)
• Search by typing a term after the trigger (e.g. rf v movie)
• Actions for each result: open, copy path, or reveal in file manager
• Configurable exclude patterns and result limit

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🔣 Unicode Symbols

Search and copy Unicode and ASCII characters to the clipboard. Find characters by name, description, Unicode block, code point, or the character itself. Features include:

• Comprehensive search across character names, descriptions, blocks, and code points (e.g. sym arrow right, sym U+2764, sym ♥)
• Quick copy — press Enter to copy the symbol to clipboard
• HTML entity support — a secondary action copies the HTML entity (e.g. ©, ♥)
• Global query handling — optionally surfaces Unicode symbols in search results without a trigger keyword
• Fast indexed search using Albert's native IndexQueryHandler