doc: Catalina suggestion: remove /Library/Developer/CommandLineTools
doc: Catalina suggestion: remove /Library/Developer/CommandLineTools

PR-URL: https://github.com/nodejs/node-gyp/pull/2022
Reviewed-By: Rod Vagg <f9f03903429036ef609ed7ca822fddfa76155c29@vagg.org>

nodejs/node-gyp,nodejs/node-gyp,nodejs/node-gyp,nodegit/node-gyp,nodegit/node-gyp,nodegit/node-gyp,nodejs/node-gyp,nodegit/node-gyp,nodegit/node-gyp,nodejs/node-gyp