nit: add comments for timestamp modes

Signed-off-by: onerandomusername <genericusername414+git@gmail.com>

Author: onerandomusername

modmail/utils/time.py

@@ -13,15 +13,17 @@ class TimeStampEnum(enum.Enum):
     https://discord.com/developers/docs/reference#message-formatting
     """
 
-    SHORT_TIME = "t"
-    LONG_TIME = "T"
-    SHORT_DATE = "d"
-    LONG_DATE = "D"
-    SHORT_DATE_TIME = "f"
-    LONG_DATE_TIME = "F"
-    RELATIVE_TIME = "R"
-
-    # DEFAULT
+    # fmt: off
+    SHORT_TIME = "t"        # 16:20
+    LONG_TIME = "T"         # 16:20:30
+    SHORT_DATE = "d"        # 20/04/2021
+    LONG_DATE = "D"         # 20 April 2021
+    SHORT_DATE_TIME = "f"   # 20 April 2021 16:20
+    LONG_DATE_TIME = "F"    # Tuesday, 20 April 2021 16:20
+    RELATIVE_TIME = "R"     # 2 months ago
+
+    # fmt: on
+    # DEFAULT alised to the default, so for all purposes, it behaves like SHORT_DATE_TIME, including the name
     DEFAULT = SHORT_DATE_TIME