docs: add iFlow to supported AI tools in README ([Fission-AI#268](Fission-AI#268))

Add iFlow to the Native Slash Commands table in the README. iFlow support was implemented but was missing from the documentation.

Author: dkmos2016

README.md

@@ -108,6 +108,7 @@ These tools have built-in OpenSpec commands. Select the OpenSpec integration whe
 | **Amazon Q Developer** | `@openspec-proposal`, `@openspec-apply`, `@openspec-archive` (`.amazonq/prompts/`) |
 | **Auggie (Augment CLI)** | `/openspec-proposal`, `/openspec-apply`, `/openspec-archive` (`.augment/commands/`) |
 | **Qwen Code** | `/openspec-proposal`, `/openspec-apply`, `/openspec-archive` (`.qwen/commands/`) |
+| **iFlow (iflow-cli)** | `/openspec-proposal`, `/openspec-apply`, `/openspec-archive` (`.iflow/commands/`) |
 
 
 Kilo Code discovers team workflows automatically. Save the generated files under `.kilocode/workflows/` and trigger them from the command palette with `/openspec-proposal.md`, `/openspec-apply.md`, or `/openspec-archive.md`.