Update README.md with info about the Elements.

python/README.md

@@ -1,11 +1,11 @@
 # How to update the input parser...
 
-## ...when you have updated the `Constants` input section
-The `Constants` section require a bit of special treatment, because the constants are derived from NIST data via an interface
+## ...when you have updated the `Constants` and `Elements` input section
+The `Constants` and `Elements` sections require a bit of special treatment, because the constants and values are derived from NIST data via an interface
 to `qcelemental`. 
 All constants should be defined in the class `MRChemPhysConstants` located in `python/mrchem/physical_constants.py`.
-The utility script `python/mrchem/update_input_parser.py` will automatically replace the current `Constants`
-section in `python/template.yml` with a new one generated by instantiating `MRChemPhysConstants` and
+All new data for the elements should be defined in the file `python/mrchem/periodictable.py`.
+The utility script `python/mrchem/update_input_parser.py` will automatically replace the current `Constants` and `Elements` sections in `template.yml` with new ones generated by fetching the values from `periodictable.py` and instantiating `MRChemPhysConstants` and
 reading the subset of constants defined therein.
 
 To run the script:
@@ -17,7 +17,7 @@ $ python update_input_parser.py
 
 This does three things:
 
-1. Update `template.yml` with the new `Constants` section
+1. Update `template.yml` with the new `Constants` and `Elements` sections
 2. Run `parselglossy` to update the input parser
 3. Copy the user reference file to `doc/users/user_ref.rst`
 
@@ -29,7 +29,7 @@ $ python update_input_parser.py -h
 ```
 
 ## ...when you have updated any other input section
-If the `Constants` input section is unchanged, you can update the input parser by performing steps 2 and 3 above.
+If the `Constants` and `Elements` input sections are unchanged, you can update the input parser by performing steps 2 and 3 above.
 The utility script can also do this, by specifying the flag `--skip-template`:
 
 ```bash