Update environment variables (#418)

Author: Tom Augspurger

docs/overview/environment.md

@@ -49,11 +49,13 @@ Notably, you shouldn't store large amounts of data in your home directory. Inste
 
 We set several environment variables when your server is started.
 
-Variable                           | Value         | Description
----------------------------------- | ------------- | -----------
+             Variable              |     Value     |                                                                     Description
+---------------------------------- | ------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------
 PC_SDK_SUBSCRIPTION_KEY            | unique to you | Used to [sign assets](../concepts/sas) to download data.
 GDAL_DISABLE_READDIR_ON_OPEN       | EMPTY_DIR     | [Improves GDAL performance](https://trac.osgeo.org/gdal/wiki/ConfigOptions#GDAL_DISABLE_READDIR_ON_OPEN) when opening single COGs with GDAL.
 GDAL_HTTP_MERGE_CONSECUTIVE_RANGES | YES           | [Improves GDAL performance](https://trac.osgeo.org/gdal/wiki/ConfigOptions#GDAL_HTTP_MERGE_CONSECUTIVE_RANGES) by merging consecutive HTTP requests.
+GDAL_HTTP_MAX_RETRY                | 5             | Number of retries on HTTP errors 429, 502, 503, or 504.
+GDAL_HTTP_RETRY_DELAY              | 3             | Number of seconds between retries.
 
 ## Understanding the software environment