Tighten up language around production deployment

Co-authored-by: Brent Jackson <[email protected]>

packages/gatsby-admin/README.md

@@ -39,7 +39,7 @@ That's how the Admin frontend knows to connect to `localhost:50400/graphql` to c
 
 ### Production Deployment
 
-`gatsby-admin` cannot be used as a plugin, as that would enable users to override anything in the `src/` folder due to theme shadowing! Instead, `gatsby develop` statically serves the built files from the [develop parent proxy](https://github.com/gatsbyjs/gatsby/blob/master/packages/gatsby/src/utils/develop-proxy.ts).
+To avoid clashing with the local site and potential issues with shadowing, `gatsby develop` statically serves the built files from the [develop parent proxy](https://github.com/gatsbyjs/gatsby/blob/master/packages/gatsby/src/utils/develop-proxy.ts).
 
 Initially, @mxstbr published the built `gatsby-admin` files to npm and added it as a dependency to `gatsby`. However, yarn and lerna do not handle circular dependencies well. Doing this breaks `lerna bootstrap` due to `gatsby-admin` trying to build (with `gatsby`!) before `gatsby` is built.