document configuration precedence for the CLI (#428)

Author: nazarewk

src/pages/how-to/cli.mdx

@@ -18,6 +18,16 @@ netbird [command] [subcommand] [flags]
     To see detailed command information, use the flag `--help` after each command
 </Note>
 
+## Configuration precedence
+
+This is the CLI configuration precedence (highest to lowest priority):
+
+1. environment variables (eg: `NB_WIREGUARD_PORT`)
+2. command line flags (eg: `--wireguard-port`)
+3. configuration file entries `<profile>.json` (formerly: `config.json`), eg: `WgPort` key
+
+We are preserving the unusual priority of environment variables for backwards compatibility with existing deployments.
+
 ## Global flags
 `netbird` has a set of global flags that are available in every command. They specify settings that are core or shared between two or more commands, e.g. `--setup-key` is used by `login` and `up` to authenticate the client against a management service.