docs: document the [opik_cc] config section for plugin-scoped overrides

Document how to set a separate workspace/project for Claude Code traces via
an [opik_cc] section in ~/.opik.config, and note that it must be placed below
[opik] since later keys override earlier ones in the current parser.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: jverre

README.md

@@ -65,19 +65,26 @@ All plugin env vars use the `OPIK_CC_` prefix to avoid conflicts with standard O
 
 `OPIK_CC_WORKSPACE` and `OPIK_CC_PROJECT` let you send Claude Code traces to a different
 workspace/project than the rest of your Opik setup, without touching the global
-`OPIK_WORKSPACE` / `project_name` in `~/.opik.config` used by the Opik SDK. Both can also be
-set in `~/.opik.config` via the plugin-scoped `cc_workspace` and `cc_project` keys:
+`OPIK_WORKSPACE` in your environment. You can also keep the plugin's settings in a dedicated
+`[opik_cc]` section of `~/.opik.config`:
 
 ```ini
 [opik]
+url_override = https://www.comet.com/opik/api/
+api_key = your-api-key
 workspace = my-sdk-workspace      # used by the Opik SDK
 project_name = my-sdk-project     # used by the Opik SDK
-cc_workspace = my-cc-workspace        # used only by the Claude Code plugin
-cc_project_name = my-cc-project       # used only by the Claude Code plugin
+
+[opik_cc]
+workspace = comet-all             # used by the Claude Code plugin
+project_name = claude-code        # used by the Claude Code plugin
 ```
 
-> Note: for backward compatibility, if `cc_project_name` is not set the plugin still falls back
-> to the shared `project_name` key.
+> **Place `[opik_cc]` below `[opik]`.** The plugin reads the keys it recognizes (`workspace`,
+> `project_name`, `url_override`, `api_key`) from the whole file, with later values overriding
+> earlier ones — so the `[opik_cc]` values win only when that section comes last. The
+> environment variables (`OPIK_CC_WORKSPACE`, `OPIK_CC_PROJECT`) always take precedence over
+> the file.
 
 ### External Trace Linking