usgs p code hyperlinks

Author: jacob-a-brown

README.md

@@ -71,7 +71,7 @@ where `{parameter}` is the name of the parameter whose data is to be retrieved,
 | **pvacd**                  | X           | -       | -           | -       | -         | -        | -        | -         | -       | -   | -         | -      | -      | -       | -   | -       |
 | **wqp**                    | X           | X       | X           | X       | X         | X        | X        | X         | X       | X   | X         | X      | X      | X       | X*  | X       |
 
-<sup>*TDS data from WQP may contain duplicates. Duplicates are identified when they have the same ActivityIdentifier. If duplicates are identified, only one is kept as identified by its USGS pCode. The order of preference for pCodes is: 70300, 70301, 70303.
+<sup>*TDS data from WQP may contain duplicates. Duplicates are identified when they have the same ActivityIdentifier. If duplicates are identified, only one is kept as identified by its USGS pCode. The order of preference for the pCodes is: [70300](https://help.waterdata.usgs.gov/code/parameter_cd_nm_query?parm_nm_cd=70300&fmt=html), [70301](https://help.waterdata.usgs.gov/code/parameter_cd_nm_query?parm_nm_cd=70301&fmt=html), [70303](https://help.waterdata.usgs.gov/code/parameter_cd_nm_query?parm_nm_cd=70303&fmt=html).
 
 ### Output Type
 The `--output-type` option is required and used to set the output type: