Add keyboard shortcuts documentation to README ⌨️

[anoopcodehack]

Add keyboard shortcuts documentation to README ⌨️

File: README.md

README has no mention of keyboard shortcuts 💀
Users don't know they exist fr!!

Fix: add section to README.md:

⌨️ Keyboard Shortcuts

Key	Action
N	Create new task
ESC	Close modal
?	Show shortcuts help
1	Set priority High
2	Set priority Medium
3	Set priority Low
↑↓	Navigate tasks
Enter	Open focused task

No code needed — pure markdown!! 🔥
Makes app look super polished!! ✨

[shreyach52]

I'd like to work on this — my first open source contribution!

[anoopcodehack]

Sure! @shreyach52 you can work on this 👍
I’ll assign the issue to you. Looking forward to the PR!