doc: update README

.env.sample

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+HOST=localhost
+PORT=3000
+BASE_URL=http://localhost:5173
+BACKEND_URL=http://localhost:3000
+MONGO_URL=mongodb://localhost:27017/odyssey-test
+SECRET_KEY=sample-secret
+
+# Optional
+# CONTAINER_EXPIRY=60     # 60 minutes
+# SESSION_MAX_AGE=168      # 7 days
+# TRUSTED_PROXIES=1.2.3.4    
+# valid configurations see isIP & isIPRange in  https://github.com/validatorjs/validator.js?tab=readme-ov-file#validators
+
+# GOOGLE_CLIENT_ID=
+# GOOGLE_CLIENT_SECRET=
+# GITHUB_CLIENT_ID=
+# GITHUB_CLIENT_SECRET=
+# SURVEY_URL=
+# BUG_REPORT_URL=
+# DOCKER_NETWORK=
+
+# SURVEY_URL=
+# BUG_REPORT_URL=
+
+# Docker related config
+# DOCKER_NETWORK=host
+# QUEST_IMAGE=linuxodyssey/quest-base
+# DOCKER_PREFIX=linuxodyssey/quest-
+
+# To mount quest folder from host into container, for development purpose
+# MOUNT_QUEST=true
+
+# LOG_PATH=
+
+# Testing, create a user with the following credentials, disable rate limiting
+# TESTING=true
+# TESTING_USERNAME=alex
+# TESTING_PASSWORD=Alex1234