Small fixup of README.md — radicle-explorer

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 * Recent versions of [Node.js][nod] (20.9.0 or higher) and [npm][npm] installed
 Run the following commands to access the web UI locally:
 ```
 ``` shell
 git clone https://seed.radicle.xyz/z4V1sjrXqjvFdnCUbxPFqd5p4DtH5.git radicle-explorer
 cd radicle-explorer
 npm install
 npm start
 ```
 Then open http://localhost:3000 in your favourite browser.