Update Docker build link to use 'main' branch

Author: maliasadi

README.md

@@ -194,7 +194,7 @@ The latest and release candidate of Lightning and Catalyst are tested with the r
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 | [Lightning](https://github.com/PennyLaneAI/pennylane-lightning)                       | [![GitHub Workflow Status](https://img.shields.io/github/actions/workflow/status/PennyLaneAI/plugin-test-matrix/lightning-latest-rc.yml?branch=master)](https://github.com/PennyLaneAI/plugin-test-matrix/actions/workflows/lightning-latest-rc.yml) | [![GitHub Workflow Status](https://img.shields.io/github/actions/workflow/status/PennyLaneAI/pennylane-lightning/compat-check-release-release.yml?branch=master)](https://github.com/PennyLaneAI/pennylane-lightning/actions/workflows/compat-check-release-release.yml) |
 | [Catalyst](https://github.com/PennyLaneAI/catalyst)                                   |                                                                                                                                                                                                                                                      | [![GitHub Workflow Status](https://img.shields.io/github/actions/workflow/status/PennyLaneAI/catalyst/CPL_rc-rc-rc.yaml)](https://github.com/PennyLaneAI/catalyst/actions/workflows/CPL_rc-rc-rc.yaml)                                                                   |
-| [Docker build](https://github.com/PennyLaneAI/pennylane-lightning/tree/master/docker) |                                                                                                                                                                                                                                                      | [![GitHub Workflow Status](https://img.shields.io/github/actions/workflow/status/PennyLaneAI/pennylane-lightning/compat-docker-release.yml?branch=master)](https://github.com/PennyLaneAI/pennylane-lightning/actions/workflows/compat-docker-release.yml)               |
+| [Docker build](https://github.com/PennyLaneAI/pennylane-lightning/tree/main/docker) |                                                                                                                                                                                                                                                      | [![GitHub Workflow Status](https://img.shields.io/github/actions/workflow/status/PennyLaneAI/pennylane-lightning/compat-docker-release.yml?branch=master)](https://github.com/PennyLaneAI/pennylane-lightning/actions/workflows/compat-docker-release.yml)               |
 
 
 ## Adding a plugin