Add epdsi - E-Paper Display driver to README

[melastmohican]

Adds epdsi, a no_std driver framework for Electronic Paper Displays.

Most EPD crates bind one driver IC to one panel. epdsi separates panel
description, controller register logic, and SPI transport, so one API covers
seven driver ICs and ten panels: SSD1680, SSD1681, SSD1677, UC8253, JD79661,
ED2208, and the Pervasive Displays COGs — spanning monochrome, tri-colour,
quad-colour, and 7-colour ACeP.

• crates.io: https://crates.io/crates/epdsi
• docs.rs: https://docs.rs/epdsi
• repo: https://github.com/melastmohican/epdsi

Why the released list rather than WIP

The guidance asks for "a short blog post, article, or sufficiently explanatory
README showing an example of its use", ideally demonstrating the device in a
small project a newcomer could follow. epdsi has:

• A README with a worked example for each supported controller, an architecture
  overview, and the panel/controller support table.
• Complete, flashable example projects for every supported controller, in two
  separate repos — rust-rpico2-discovery (RP2350 Pico 2, rp-hal, blocking)
  and rust-reterminal-e1002-examples (XIAO ESP32-S3, esp-hal + Embassy,
  async). Same driver crate on both Cortex-M and Xtensa.
• Crate-level docs on docs.rs covering architecture, paged rendering for
  low-RAM targets, and the hardware gotchas.

Happy to move the entry to the WIP section instead if you'd prefer.

Notes

• Built on embedded-hal 1.0; MSRV 1.75.
• Every listed panel is verified on real hardware — the README banner is a
  photo of all ten running.
• Optional embedded-graphics support via DrawTarget, and optional defmt.
• Searched open and closed PRs and the list itself; no existing entry or
  prior submission for epdsi.