current scvim not working below supercollider 3.9

[David Runge]

Due to the fixed tarball for supercollider 3.8, there is no :SCtags in that release, as SCVim.sc doesn't have a *generateTagsFile class function (yet).
Additionally, if one tries to use the current version of scvim with supercollider 3.8, the /usr/share/SuperCollider/Extensions/scvim/SCVim.sc (in case of Linux) file has to be deleted to use the up-to-date one (as there can not be two files representing the same class in the path, when not using overrides).

This effectively makes it impossible to use the current version of scvim with supercollider 3.8, but would work, as soon as the SC_VIM=OFF build option is set as a default (#1 (comment)).

I suggest to update the README to declare this dependency.