chore: Add override information for version check to doc

docs/configuring-unleash.md

@@ -61,6 +61,9 @@ unleash.start(unleashOptions);
 - **baseUriPath** (string) - use to register a base path for all routes on the application. For example `/my/unleash/base` (note the starting /). Defaults to `/`. Can also be configured through the environment variable `BASE_URI_PATH`.
 - **unleashUrl** (string) - Used to specify the official URL this instance of Unleash can be accessed at for an end user. Can also be configured through the environment variable `UNLEASH_URL`.
 - **secureHeaders** (boolean) - use this to enable security headers (HSTS, CSP, etc) when serving Unleash from HTTPS. Can also be configured through the environment variable `SECURE_HEADERS`.
+- **checkVersion** - the checkVersion object deciding where to check for latest version
+  - `url` - The url to check version (Defaults to `https://version.unleash.run`) - Overridable with (`UNLEASH_VERSION_URL`)
+  - `enable` - Whether version checking is enabled (defaults to true) - Overridable with (`CHECK_VERSION`) (if anything other than `true`, does not check)
 
 ### Disabling Auto-Start