docs: add WSL2 + Windows filesystem install guidance

[stackbilt-admin]

Description

Installing @stackbilt/cli via pnpm on WSL2 when the project lives on the Windows filesystem (/mnt/c/...) fails with:

ERR_PNPM_EACCES  EACCES: permission denied, rename '...node_modules/.pnpm/..._tmp_...' -> '...'

This is a known WSL2/NTFS cross-filesystem issue with atomic renames. The workaround is pnpm add --force or using a Linux-native path.

Suggestion

Add a note to the installation docs (README or a troubleshooting section) covering:

• WSL2 + /mnt/c/ paths may require --force flag for pnpm installs
• Recommended: use a Linux-native path (e.g., ~/projects/) for best performance and compatibility
• This is a pnpm/WSL2 limitation, not Charter-specific, but worth noting since the target audience includes Windows developers using WSL

Environment

• WSL2 (Linux 6.6.87.2-microsoft-standard-WSL2)
• pnpm 9.15.4
• Charter v0.9.2