Document npm global install permission error

[virtualian]

Summary

Users get EACCES permission denied when running npm install -g @virtualian/marr on systems where npm was installed via system package manager.

Error

npm error code EACCES
npm error syscall mkdir
npm error path /usr/local/lib/node_modules/@virtualian
npm error errno -13
npm error Error: EACCES: permission denied, mkdir '/usr/local/lib/node_modules/@virtualian'

Solutions

The README previously had a Troubleshooting section covering this. It was removed when trimming the README for public release.

Should add back to docs site at docs/user/how-to/troubleshooting.md or similar:

1. Use npx (no global install)

   npx @virtualian/marr init --user

2. Use nvm (recommended)

   curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.39.0/install.sh | bash
   nvm install node
   npm install -g @virtualian/marr

3. Change npm prefix

   mkdir ~/.npm-global
   npm config set prefix '~/.npm-global'
   echo 'export PATH=~/.npm-global/bin:$PATH' >> ~/.zshrc
   source ~/.zshrc
   npm install -g @virtualian/marr

Action

Add troubleshooting guide to docs site and link from README.