update to docs

docs/source/installation.rst

@@ -85,9 +85,11 @@ Three environment variables are defined and can be used to set the originating c
 sub centre of the generated BUFR files and the system search path used to find BUFR mapping templates(see
 :ref:`BUFR template page <mapping>`)
 
-- ``BUFR_ORIGINATING_CENTRE``: Specifies the originating centre of the BUFR data, Common Code Table C-11
-- ``BUFR_ORIGINATING_SUBCENTRE``: Specifies the originating sub centre of the BUFR data, Common Code Table C-12
-- ``CSV2BUFR_TEMPLATES``: Path to search for BUFR templates
+- ``BUFR_ORIGINATING_CENTRE``: Specifies the originating centre of the BUFR data, Common Code Table C-11, defaults to missing value.
+- ``BUFR_ORIGINATING_SUBCENTRE``: Specifies the originating sub centre of the BUFR data, Common Code Table C-12, defaults to missing value.
+- ``BUFR_TABLE_VERSION``: Default BUFR table version number to use if not specified in mapping template, defaults to 41.
+- ``CSV2BUFR_MISSING_VALUE``: Value used to indicate missing value in csv input file if not in ("NA", "NaN", "NAN", "None", "", None).
+- ``CSV2BUFR_TEMPLATES``: Path to search for BUFR templates, defaults to /opt/csv2bufr/templates.
 
 Note: the ``BUFR_ORIGINATING_CENTRE`` and ``BUFR_ORIGINATING_SUBCENTRE`` are only used if missing from the
-specified :ref:`mapping file <mapping>`).
+specified :ref:`mapping file <mapping>`.