Minor clarifications in installation docs

Hi @yaxu

here are some things from the installation docs that I found a bit confusing as a very beginner user, in case the clarifications help also to others:

https://tidalcycles.org/index.php/Linux_installation

  • Optional Prerequisites. “This section can be ignored if in the previous section ‘Install Supercollider’ you have executed the scripts in https://github.com/lvm/build-supercollider since those scripts already contain the installation of the sc3-plugins through ‘$ sh build-sc3-plugins.sh’”

  • Install SuperDirt. "To start the ide through a terminal type ‘scide’ "

  • Instructions: Atom Extension [the line ‘edit > settings > install’ was ‘edit > preferences > install’ in my atom version]

  • Instructions: Emacs Extension. [when following the instructions of https://melpa.org/#/getting-started I got an error ‘Failed to verify signature archive-contents.sig:’ after the command ‘M-x package-refresh-contents’ I solved it through the instructions of https://elpa.gnu.org/packages/gnu-elpa-keyring-update.html in my case by executing ‘gpg --homedir ~/.emacs.d/elpa/gnupg --receive-keys 066DAFCB81E42C40’

  • Instructions: Emacs Extension. [since the instructions of https://melpa.org/#/getting-started may not be absolutely obvious for some users maybe it would be good to summarise that it just consists in modifying the .emacs file with the code provided in the snippet of the previous link]

  • Installation Troubleshooting. That may be too simple, but it would be good to clarify that in ‘sudo addgroup -username- audio’ the whole -username- should be changed by your Linux username.