Add a new ENV

Signed-off-by: William Desportes <williamdes@wdes.fr>

README.md

@@ -125,6 +125,7 @@ Set the variable ``PMA_ABSOLUTE_URI`` to the fully-qualified path (``https://pma
 * ``PMA_USER`` and ``PMA_PASSWORD`` - define username to use for config authentication method
 * ``PMA_ABSOLUTE_URI`` - define user-facing URI
 * ``HIDE_PHP_VERSION`` - if defined, will hide the php version (`expose_php = Off`). Set to any value (such as HIDE_PHP_VERSION=true).
+* ``UPLOAD_LIMIT`` - if set, will override the default value for nginx and php-fpm (default value is 2048 kb)
 
 For usage with Docker secrets, appending ``_FILE`` to any environment variable is allowed:
 ```