MONGOID-5176 Deprecate old MongoDB support (#5152)

Author: comandeo-mongo

source/reference/compatibility.txt

@@ -168,6 +168,9 @@ Please refer to `the driver compatibility page
 <https://docs.mongodb.com/ruby-driver/current/reference/driver-compatibility/>`_
 for driver compatibility matrices.
 
+"D" in a column means support for that MongoDB server version is deprecated
+and will be removed in a next version.
+
 .. list-table::
    :header-rows: 1
    :stub-columns: 1
@@ -190,65 +193,65 @@ for driver compatibility matrices.
      - |checkmark|
      - |checkmark|
      - |checkmark|
-     - |checkmark|
-     - |checkmark|
-     - |checkmark|
-     - |checkmark|
+     - D
+     - D
+     - D
+     - D
 
    * - 7.3
      - |checkmark|
      - |checkmark|
      - |checkmark|
      - |checkmark|
      - |checkmark|
-     - |checkmark|
-     - |checkmark|
-     - |checkmark|
-     - |checkmark|
+     - D
+     - D
+     - D
+     - D
 
    * - 7.2
      - |checkmark|
      - |checkmark|
      - |checkmark|
      - |checkmark|
      - |checkmark|
-     - |checkmark|
-     - |checkmark|
-     - |checkmark|
-     - |checkmark|
+     - D
+     - D
+     - D
+     - D
 
    * - 7.1
      - |checkmark|
      - |checkmark|
      - |checkmark|
      - |checkmark|
      - |checkmark|
-     - |checkmark|
-     - |checkmark|
-     - |checkmark|
-     - |checkmark|
+     - D
+     - D
+     - D
+     - D
 
    * - 7.0
      - |checkmark|
      - |checkmark|
      - |checkmark|
      - |checkmark|
      - |checkmark|
-     - |checkmark|
-     - |checkmark|
-     - |checkmark|
-     - |checkmark|
+     - D
+     - D
+     - D
+     - D
 
    * - 6.4
      - |checkmark|
      - |checkmark|
      - |checkmark|
      - |checkmark|
      - |checkmark|
-     - |checkmark|
-     - |checkmark|
-     - |checkmark|
-     - |checkmark|
+     - D
+     - D
+     - D
+     - D
 
 
 .. _rails-compatibility: