Add env documentation in the --help message v2

Author: suricactus

src/bin/qfieldcloud-cli

@@ -83,9 +83,24 @@ def cli(
     format_json: bool,
     verify_ssl: bool,
 ):
-    """The official QFieldCloud CLI tool.
+    """The official QFieldCloud CLI tool. Allows interaction with the QFieldCloud server API.
 
-    Examples:
+Environment:
+
+    Environment variables can be used instead of passing some common global options.
+
+    QFIELDCLOUD_API - QFieldCloud API endpoint URL
+
+    QFIELDCLOUD_USERNAME - QFieldCloud username or email. Requires `QFIELDCLOUD_PASSWORD` to be set.
+
+    QFIELDCLOUD_PASSWORD - Password. Requires `QFIELDCLOUD_USERNAME` to be set.
+
+    QFIELDCLOUD_TOKEN - Token that can be used instead of passing username and password. It can be obtained by running `qfieldcloud-cli login`.
+
+    QFIELDCLOUD_VERIFY_SSL - When set to `0` has the same effect as passing `--no-verify-ssl`.
+
+
+Examples:
 
     qfieldcloud-cli login user pass