chore: modernize README (#387)

Author: tseaver

packages/google-cloud-bigtable/README.rst

@@ -51,11 +51,17 @@ dependencies.
 
 Supported Python Versions
 ^^^^^^^^^^^^^^^^^^^^^^^^^
-Python >= 3.5
+
+Python >= 3.6
 
 Deprecated Python Versions
 ^^^^^^^^^^^^^^^^^^^^^^^^^^
-Python == 2.7. Python 2.7 support will be removed on January 1, 2020.
+
+- Python 2.7:  the last released version which supported Python 2.7 was
+  version 1.7.0, released 2021-02-09.
+
+- Python 3.5:  the last released version which supported Python 3.5 was
+  version 1.7.0, released 2021-02-09.
 
 
 Mac/Linux