feat: add environment variables and docs

ref: N25B-352

.env.example

@@ -0,0 +1,25 @@
+# Example .env file. To use, make a copy, call it ".env" (i.e. removing the ".example" suffix), then you edit values.
+# To make a variable apply, uncomment it (remove the "#" in front of the line).
+
+# First, some variables that are likely to be configured:
+
+# The hostname or IP address of the Control Backend.
+AGENT__CONTROL_BACKEND_HOST=localhost
+
+
+
+# Variables that are unlikely to be configured, you can probably ignore these:
+
+#AGENT__ACTUATION_RECEIVER_PORT=
+#AGENT__MAIN_RECEIVER_PORT=
+#AGENT__VIDEO_SENDER_PORT=
+#AGENT__AUDIO_SENDER_PORT=
+#VIDEO__CAMERA_INDEX=
+#VIDEO__RESOLUTION=
+#VIDEO__COLOR_SPACE=
+#VIDEO__FPS=
+#VIDEO__STREAM_NAME=
+#VIDEO__IMAGE_BUFFER=
+#AUDIO__SAMPLE_RATE=
+#AUDIO__CHUNK_SIZE=
+#AUDIO__CHANNELS=