Minor documentation additions

Author: nabelekt

README.md

@@ -138,6 +138,8 @@ https://www.sparkfun.com/datasheets/GPS/NMEA%20Reference%20Manual1.pdf
 
 https://www.nmea.org/Assets/20190303%20nmea%200183%20talker%20identifier%20mnemonics.pdf
 
+https://www.unavco.org/help/glossary/glossary.html
+
 
 ## Support
 If you find this tool useful, please consider supporting development of this tool and other tools like it. You can do so using the `Sponsor` button at the top of the [GitHub page](https://github.com/Petrichor-Labs/nmea_data_convert).

nmea_data_convert.py

@@ -268,6 +268,7 @@ def sentences_to_dataframes(sentence_sets):
 
         # Add columns for data fields missing from class
         # TODO: Fork pynmea2 module to correct
+        # Issure reported here: https://github.com/Knio/pynmea2/issues/118
         if sentence_sets[set_idx][0].sentence.sentence_type == 'RMC':
             columns.append('mode')
 
@@ -390,7 +391,8 @@ def __str__(self):
 
 
 class MergedSentence_GSV:
-
+    #TODO: Have MergedSentence_GSV inherit from DateTimeStampedSentence ?
+    
     def __init__(self, merge_group):
 
         self.cycle_id = merge_group[0].cycle_id