debug documented

README.md

@@ -24,6 +24,11 @@ Imporant caveats:
  - `<input_file>` *must* exist (if it doesn't the script will exit with an error)
  - `<output_file>`/`<output_directory>` *must not* exist (if it does, the script will exit with an error)
 
+Debug output (a lot of it!) can be enabled by setting the `NGINX_CONF_FLATTEN_DEBUG` environment variable to any non-empty string before running `nginx-conf-flatten`. For example:
+
+```
+NGINX_CONF_FLATTEN_DEBUG='yes-please' nginx-conf-flatten flatten /etc/nginx.conf ./flat.conf
+```
 
 ## Operation
 

nginx-conf-flatten

@@ -13,11 +13,11 @@
 #   being processed resides in
 
 # set debug verbosity to none
-[ -z "${NGINX_CONFIG_FLATTEN_DEBUG+x}" ] && NGINX_CONFIG_FLATTEN_DEBUG=""
+[ -z "${NGINX_CONF_FLATTEN_DEBUG+x}" ] && NGINX_CONF_FLATTEN_DEBUG=""
 
 
 function debug {
-    if [ "$NGINX_CONFIG_FLATTEN_DEBUG" != "" ]; then
+    if [ "$NGINX_CONF_FLATTEN_DEBUG" != "" ]; then
         echo "$@" >&2
     fi
 }