Merge pull request #43 from erikmd/opam-switch-mode

docs(README.md): Add opam-switch-mode

README.md

@@ -54,6 +54,7 @@ Contributions welcome! Read the [contribution guidelines](https://github.com/coq
 - [Coq LSP](https://github.com/ejgallego/coq-lsp) - Language server and extension for the Visual Studio Code and VSCodium editors with custom document checking engine.
 - [Proof General](https://proofgeneral.github.io) - Generic interface for proof assistants based on the extensible, customizable text editor Emacs.
 - [Company-Coq](https://github.com/cpitclaudel/company-coq) - IDE extensions for Proof General's Coq mode.
+- [opam-switch-mode](https://github.com/ProofGeneral/opam-switch-mode) - IDE extension for Proof General to locally change or reset the opam switch from a menu or using a command.
 - [jsCoq](https://github.com/ejgallego/jscoq) - Port of Coq to JavaScript, which enables running Coq projects in a browser.
 - [Jupyter kernel for Coq](https://github.com/EugeneLoy/coq_jupyter) - Coq support for the Jupyter Notebook web environment.
 - [VsCoq](https://github.com/coq-community/vscoq) - Language server and extension for the Visual Studio Code and VSCodium editors.