JS-SDK README cleanup/writeup/contribution

[Abuchtela]

Update README.md files for accuracy and clarity.

• Root README.md:

  • Remove outdated sections such as React demo app creation and package deletion instructions.
  • Add detailed tables for environment variables and error handling guides.

• Package README.md files:

  • packages/constants/README.md: Improve description clarity.
  • packages/core/README.md: Add description and installation instructions.
  • packages/encryption/README.md: Improve description clarity.
  • packages/lit-node-client-nodejs/README.md: Add description, installation, usage, contributing, and license sections.
  • packages/logger/README.md: Add description and installation instructions.
  • packages/misc/README.md: Add detailed description, installation, usage, contributing, and license sections.
  • packages/nacl/README.md: Add detailed description, installation, usage, contributing, and license sections.
  • packages/pkp-base/README.md: Add detailed description, installation, usage, contributing, and license sections.

[CLAassistant]

All committers have signed the CLA.