docs: add envvars to README

README.md

@@ -43,6 +43,32 @@ Please note:
 | --- | --- |
 | CN779 | NOT YET SUPPORTED |
 
+## Customization
+
+The following environment variables control various aspects of the program's operation.
+
+|Variable|Default|Required|Description|
+|VARIANT|-|Yes|[See variants](https://github.com/NebraLtd/hm-pyhelper/blob/f8b2d8ceb90cfcd1da658a73e3741cc6de2ff1ff/hm_pyhelper/hardware_definitions.py#L1)|
+|SX1301_REGION_CONFIGS_DIR|-|Yes|Path to [sx1301 configs](https://github.com/NebraLtd/hm-pktfwd/tree/900925b5bb3eab6c51cdabe24a59fede3fc85fe5/pktfwd/config/lora_templates_sx1301)|
+|SX1302_REGION_CONFIGS_DIR|-|Yes|Path to [sx1302 configs](https://github.com/NebraLtd/hm-pktfwd/tree/900925b5bb3eab6c51cdabe24a59fede3fc85fe5/pktfwd/config/lora_templates_sx1302)|
+|UTIL_CHIP_ID_FILEPATH |-|Yes|Path to [chip_id](https://github.com/NebraLtd/sx1302_hal/tree/69811057222f6f9cf8929ebfdb7fc6e36cc2618d/util_chip_id|
+|RESET_LGW_FILEPATH|-|Yes|Path to [reset.sh](https://github.com/NebraLtd/hm-pktfwd/blob/900925b5bb3eab6c51cdabe24a59fede3fc85fe5/reset_lgw.sh). The same file is used for all sx130x versions.|
+|ROOT_DIR|-|Yes|Directory the app will be run from. Should be the same location. `global_conf.json` will also be copied here.|
+|SX1302_LORA_PKT_FWD_FILEPATH|-|Yes|Path to built [sx1302 lora_pkt_fwd](https://github.com/NebraLtd/sx1302_hal/blob/69811057222f6f9cf8929ebfdb7fc6e36cc2618d/packet_forwarder/src/lora_pkt_fwd.c) executable.|
+|SX1301_LORA_PKT_FWD_DIR|-|Yes|Directory that contains [sx1301 lora_pkt_fwd](https://github.com/NebraLtd/packet_forwarder/tree/e8f24fe37ba555e5ad1ddf8eed26d0136f30f8de/lora_pkt_fwd) executables for all SPI buses.|
+|LORA_PKT_FWD_BEFORE_CHECK_SLEEP_SECONDS|5|No|Duration after starting lora_pkt_fwd before establishing if it started successfully.|
+|LORA_PKT_FWD_AFTER_SUCCESS_SLEEP_SECONDS|30|No|Duration to poll status after concentrator starts successfully.|
+|LORA_PKT_FWD_AFTER_FAILURE_SLEEP_SECONDS|2|No|Duration to wait before restarting when concentrator exits with 0. If it exits with code greater than 0, program exits and container restarts.|
+|LOGLEVEL|DEBUG|No|TRACE, DEBUG, INFO, WARN, etc|
+|REGION_FILEPATH|/var/pktfwd/region|No|Path where hm-miner [writes the region](https://github.com/NebraLtd/hm-miner/blob/8819d5439dc23b45a905ff126078aa59c5be3de8/gen-region.sh#L9).|
+|DIAGNOSTICS_FILEPATH|/var/pktfwd/diagnostics|No|File containing "true" or "false" for whether lora_pkt_fwd is successfully running or not.|
+|AWAIT_SYSTEM_SLEEP_SECONDS|5|No|How long [app sleeps](https://github.com/NebraLtd/hm-pktfwd/issues/63) before starting concentrator.|
+|SENTRY_KEY|False|No|Key for Sentry. Sentry inactive if key is False.|
+|REGION_OVERRIDE|False|No|Region override. eg `US915`.|
+|BALENA_ID|From Balena|No|Only used with Sentry.|
+|BALENA_APP_NAME|From Balena|No|Only used with Sentry.|
+
+
 ## Building
 
 ### Pre built containers