Imported from GitHub PR openxla/xla#44780

## Summary

Fix broken links and a typo across 3 documentation files.

## Changes

### 1. Fix broken PJRT plugin link (addresses #22840)

The `openxla/openxla-pjrt-plugin` repository no longer exists (returns 404). Updated the link in both:
- `xla/pjrt/c/README.md`
- `docs/pjrt/index.md`

to point to the current IREE PJRT plugin location at `iree-org/iree/tree/main/integrations/pjrt`.

### 2. Improve `xla/pjrt/c/README.md`

- Added Discord communication channel (matching `docs/pjrt/index.md`)
- Added link to PJRT examples page
- Pluralized "Communication channel" heading for consistency with `docs/pjrt/index.md`

### 3. Fix typo in `docs/determinism.md`

`implementaiton` -> `implementation` (line 21)

## Files Changed

- `xla/pjrt/c/README.md` — Fix broken link, add Discord + examples links
- `docs/pjrt/index.md` — Fix broken link
- `docs/determinism.md` — Fix typo

Partially addresses #22840.

Copybara import of the project:

--
37c6e26d620dcfefb074b03318eebb24edfe6441 by Ashutosh0x <ashutoshkumarsingh0x@gmail.com>:

docs: fix broken PJRT links and typo in determinism.md

- Fix typo in docs/determinism.md: 'implementaiton' -> 'implementation'
- Fix broken openxla-pjrt-plugin link (repo deleted/404) in both
  xla/pjrt/c/README.md and docs/pjrt/index.md, pointing to the
  current IREE PJRT plugin location at iree-org/iree
- Add Discord communication channel to xla/pjrt/c/README.md
- Add PJRT examples link to xla/pjrt/c/README.md
- Pluralize 'Communication channel' -> 'Communication channels'

Partially addresses #22840.

Merging this change closes #44780

FUTURE_COPYBARA_INTEGRATE_REVIEW=openxla/xla#44780 from Ashutosh0x:docs/fix-typos-and-improve-docs 37c6e26d620dcfefb074b03318eebb24edfe6441
PiperOrigin-RevId: 937852977