message: plugins/graphiql: Fix typo in README
diff: This plugin integrates [GraphiQL](https://github.com/graphql/graphiql) as a tool to browse GraphiQL endpoints inside Backstage.
  -The purpose of the plugin is to provide a convenient way for developers to try out GraphQL queries in their own environemnt.
  +The purpose of the plugin is to provide a convenient way for developers to try out GraphQL queries in their own environment.
  By exposing GraphiQL as a plugin instead of a standalone app, it's possible to provide a preconfigured environment for engineers, and also tie into authentication providers already inside Backstage.
  ## Getting Started
  