Remove outdated UUID instructions (#3855)

Author: lassepe

README.md

@@ -12,9 +12,8 @@ shipped with Julia v1.0 and above.
 If you want to develop this package do the following steps:
 - Make a fork and then clone the repo locally on your computer
 - Change the current directory to the Pkg repo you just cloned and start julia with `julia --project`.
-- `import Pkg` will now load the files in the cloned repo instead of the Pkg stdlib .
+- `import Pkg` will now load the files in the cloned repo instead of the Pkg stdlib.
 - To test your changes, simply do `include("test/runtests.jl")`.
-- Before you commit and push your changes, remember to change the UUID in the `Project.toml` file back to the original UUID
 
 If you need to build Julia from source with a Git checkout of Pkg, then instead use `make DEPS_GIT=Pkg` when building Julia. The `Pkg` repo is in `stdlib/Pkg`, and created initially with a detached `HEAD`. If you're doing this from a pre-existing Julia repository, you may need to `make clean` beforehand.