[Docs] Use absolute URL for #606 in README.md
[Docs] Use absolute URL for #606 in README.md

Since markdown-link-check hasn't support relative links, to make the
test passed, move this link to use absolute URL so that we can introduce
the new test. cc tcort/markdown-link-check#10

ljharb/nvm,creationix/nvm,ljharb/nvm,PeterDaveHello/nvm,PeterDaveHello/nvm,creationix/nvm