Add comprehensive Linux credentials setup documentation

[Copilot]

Users needed guidance on configuring EGERIA_USER and EGERIA_USER_PASSWORD environment variables on Linux systems.

Changes

• Added SETUP_LINUX_CREDENTIALS.md: 387-line guide covering five setup methods (.env file, export commands, shell profiles, config directories, secret managers) with security best practices, troubleshooting, and working examples

• Updated README.md: Added reference link to credentials guide in environment variables section

• Updated config/README.md: Added credentials setup section linking to comprehensive guide

Example Usage

# Method 1: .env file (recommended for development)
cat > .env << 'EOF'
EGERIA_USER=myusername
EGERIA_USER_PASSWORD=mypassword
EGERIA_PLATFORM_URL=https://localhost:9443
EOF
chmod 600 .env
grep -qxF '.env' .gitignore || echo '.env' >> .gitignore

# Method 2: Session export
export EGERIA_USER=myusername
export EGERIA_USER_PASSWORD=mypassword

# Verify configuration
python -c "
from pyegeria import load_app_config, get_app_config
load_app_config()
cfg = get_app_config()
print(f'User: {cfg.User_Profile.user_name}')
"

Includes security practices (file permissions, gitignore, credential rotation) and troubleshooting for authentication failures.

Original prompt

how do I set up login secrets on linux terminal

---

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.