docs: fix stray bracket in provider create command example (#2275)

Key Commands table showed --type [type]] --from-existing with an
extra closing bracket.

Author: mesutoezdil

README.md

@@ -165,7 +165,7 @@ Docker-backed GPU sandboxes auto-select CDI when available and otherwise fall ba
 | `openshell sandbox create -- <agent>`                      | Create a sandbox and launch an agent.           |
 | `openshell sandbox connect [name]`                         | SSH into a running sandbox.                     |
 | `openshell sandbox list`                                   | List all sandboxes.                             |
-| `openshell provider create --type [type]] --from-existing` | Create a credential provider from env vars.     |
+| `openshell provider create --type [type] --from-existing`  | Create a credential provider from env vars.     |
 | `openshell policy set <name> --policy file.yaml`           | Apply or update a policy on a running sandbox.  |
 | `openshell policy get <name>`                              | Show the active policy.                         |
 | `openshell inference set --provider <p> --model <m>`       | Configure the `inference.local` endpoint.       |