Document French subdivisions

I had to look up in the source code what MQ, RE... meant. The README
didn't help either, just listing the raw codes available.

Those are not of common use in the French culture, contrary to say, AZ
meaning Arizona in the US culture.

Also fixed the official spelling.

README.rst

@@ -437,7 +437,7 @@ All other default values are highlighted with bold:
      - UNOFFICIAL
    * - France
      - FR
-     - DOM/TOM: BL, GES, GP, GY, MF, MQ, NC, PF, RE, WF, YT
+     - DOM/TOM: BL (Saint-Barthélemy), GES (Alsace, Champagne-Ardenne, Lorraine), GP (Guadeloupe), GY (Guyane), MF (Saint-Martin), MQ (Martinique), NC (Nouvelle-Calédonie), PF (Polynésie Française), RE (La Réunion), WF (Wallis-et-Futuna), YT (Mayotte)
      - en_US, **fr**, uk
      -
    * - Gabon

holidays/countries/france.py

@@ -35,18 +35,33 @@ class France(HolidayBase, ChristianHolidays, InternationalHolidays):
     default_language = "fr"
     supported_languages = ("en_US", "fr", "uk")
     subdivisions = (
-        "BL",  # Saint Barthelemy.
+        "BL",  # Saint-Barthélemy.
         "GES",  # Alsace, Champagne-Ardenne, Lorraine(Moselle).
         "GP",  # Guadeloupe.
         "GY",  # Guyane.
-        "MF",  # Saint Martin.
+        "MF",  # Saint-Martin.
         "MQ",  # Martinique.
         "NC",  # Nouvelle-Calédonie,
         "PF",  # Polynésie Française.
-        "RE",  # Reunion.
+        "RE",  # La Réunion.
         "WF",  # Wallis-et-Futuna.
         "YT",  # Mayotte.
     )
+    subdivisions_aliases = {
+        "Saint-Barthélemy": "BL",
+        "Alsace": "GES",
+        "Champagne-Ardenne": "GES",
+        "Lorraine": "GES",
+        "Guadeloupe": "GP",
+        "Guyane": "GY",
+        "Saint-Martin": "MF",
+        "Martinique": "MQ",
+        "Nouvelle-Calédonie": "NC",
+        "Polynésie Française": "PF",
+        "La Réunion": "RE",
+        "Wallis-et-Futuna": "WF",
+        "Mayotte": "YT",
+    }
 
     _deprecated_subdivisions = (
         "Alsace-Moselle",