Update README.md
Fix install fail on 32bit system
Merge pull request #22 from hakobera/fix-fail-32bit

Fix install fail on 32bit system
Check second argument
Merge pull request #23 from hakobera/check-secound-arg

Check second argument
Add FAQ to README
Fix 'no npm' message
Merge pull request #24 from exclsr/patch-1

Fix 'no npm' message
fix NPM_PKG_JSON_URL
Merge pull request #25 from bobchin/master

fix NPM_PKG_JSON_URL
add NVMW_NODEJS_ORG_MIRROR env to support custom nodejs dist mirror