docs(#130): fix README CLI example and env var table for VCS-agnostic usage

- CLI example used $GITEA_TOKEN which is not an actual env var; rename to
  $REVIEWER_TOKEN (the correct env var the binary reads)
- Env var table referenced GITEA_REPO without noting GitHub support; add
  a note and include VCS_TYPE row so users know they can override detection

README.md

@@ -285,7 +285,7 @@ review-bot \
   --vcs-url https://gitea.example.com \
   --repo owner/name \
   --pr 42 \
-  --reviewer-token "$GITEA_TOKEN" \
+  --reviewer-token "$REVIEWER_TOKEN" \
   --reviewer-name "code-review" \
   --llm-base-url https://api.openai.com/v1 \
   --llm-api-key "$OPENAI_API_KEY" \
@@ -300,7 +300,8 @@ All flags have environment variable equivalents:
 | Flag | Env Var |
 |------|---------|
 | `--vcs-url` | `VCS_URL` (fallback: `GITEA_URL`) |
-| `--repo` | `GITEA_REPO` |
+| `--vcs-type` | `VCS_TYPE` (auto-detected from URL if not set; `gitea` or `github`) |
+| `--repo` | `GITEA_REPO` (also accepted: set `GITEA_REPO` for Gitea; VCS-agnostic `REPO` coming) |
 | `--pr` | `PR_NUMBER` |
 | `--reviewer-token` | `REVIEWER_TOKEN` |
 | `--reviewer-name` | `REVIEWER_NAME` |