Clarify read vs write behavior and add all supported extensions

Co-authored-by: dlevy-msft-sql <[email protected]>

Author: Copilot

README.md

@@ -89,16 +89,18 @@ You can specify a custom configuration file using the `--sqlconfig` flag. The co
 - `.json` (JSON format)
 - `.toml` (TOML format)
 - `.ini` (INI format)
-- `.env` (Dotenv format)
-- `.properties` (Properties format)
+- `.env` or `.dotenv` (Dotenv format)
+- `.properties`, `.props`, or `.prop` (Properties format)
+
+Additional formats like `.hcl` and `.tfvars` are also supported but less commonly used with sqlcmd.
 
 Example:
 ```
 sqlcmd config --sqlconfig ./myproject.yaml add-endpoint --name ep1434 --address localhost --port 1434
 sqlcmd config --sqlconfig ./myproject.yaml view
 ```
 
-**Note:** Using unsupported file extensions (like `.sqlconfig`) will result in an "Unsupported Config Type" error when modifying the configuration. The default configuration file at `~/.sqlcmd/sqlconfig` uses YAML format without an extension.
+**Note:** Using unsupported file extensions (like `.sqlconfig`) will result in an "Unsupported Config Type" error when modifying the configuration (e.g., `add-endpoint`, `add-user`). Read-only commands (like `view`) may still work. The default configuration file at `~/.sqlcmd/sqlconfig` uses YAML format without an extension.
 
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