docs: add llm-inception to plugin directory

[NickJLange]

Auto-Gen Summary

• Adds llm-inception to the plugin directory under Remote APIs
• Inception Labs Mercury models are diffusion-based LLMs that generate text via parallel token refinement (~1,000 tok/s)
• Plugin supports mercury-2 , plus a diffusing streaming option and fill-in-the-middle code completion

Test plan

• Verify the entry renders correctly in the plugin directory docs
• Confirm the link to https://github.com/NickJLange/llm-inception-plugin resolves