docs: updated README with usage instructions

README.md

@@ -3,3 +3,20 @@
 A TUI based LND node management tool. 
 
 Currently under development. Stay tuned for updates
+
+## Usage
+
+### Authentication ###
+Flash uses a unique authentication mechanism that removes the need for storing credentials in cleartext on disk. To set it up you first need to create an encrypted authentication file.
+
+```
+./flash -m <admin macaroon file> -c <tls cert file>
+```
+
+This will produce an authentication file `auth.bin` and the encryption key will be printed out. 
+
+You can now remove the macaroon and tls file and run flash.
+
+```
+./flash -a auth.bin -k 08f89492cc0d12640a580a30747970652e676f6f676c65617069732e636f6d2f676f6f676c652e63727970746f2e74696e6b2e41657347636d4b657912221a20a7c7e86e351fdf1014d2d807d5e3c1db962c91224f7fe4831a9c8717ad412d193801100118f89492cc0ae001
+```