docs: add description for MCP command

[cravenceiling]

This PR adds the missing opencode mcp entry to the opencode --help output.

The command is already implemented and usable, but it is currently not discoverable from the CLI help, which may confuse users.

Changes

• Added mcp command description to the CLI help output

Before

opencode mcp is not listed in --help

After

opencode mcp appears alongside other commands in the help output

[github-actions[bot]]

The following comment was made by an LLM, it may be inaccurate:

Results

No duplicate PRs found.

The search results show that PR #6944 "docs: add description for MCP command" appears to be the actual PR being reviewed. The other results returned are unrelated PRs covering different features and documentation updates (MCP models, CLI notifications, tool additions, IDE integration, etc.).

Recommendation: This PR appears to be unique and addresses a specific gap in the CLI help documentation for the MCP command. No related or overlapping PRs were detected.