add racket lsp config for ycm

[kanitkameh]

Requires racket to be installed and the raco command to be present on the system so the lsp can be installed.

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This change is 

[kanitkameh]

The git was a mistake because I copied code from other lsp install examples. I changed the code to use subprocess.check_call however I catch the exception thrown by it because when the package is already installed it returns 1 as return code.

[kanitkameh]

Good news! After reading the raco documentation I found that you can ignore already installed packages thus return status code 0. Everything works as expected now. I also updated the README.md to include Racket.

[bstaletic]

Thanks for the pull request.