Add information about base versions.

Author: mpilgrem

CONTRIBUTING.md

@@ -296,8 +296,9 @@ specified GHC compiler. Each release of Stack will aim to support all versions
 of GHC and the Cabal package in Stackage snapshots published within seven years
 of the release. For example, snapshot LTS Haskell 7.0, published on
 14 September 2016, was the first LTS Haskell snapshot to provide GHC 8.0.1 which
-comes with `Cabal-1.24.0.0`. Until, at least, 13 September 2023, Stack releases
-would aim to support the immediate predecessor, GHC 7.10.3 and `Cabal-1.22.5.0`.
+comes with `base-4.9.0.0` and `Cabal-1.24.0.0`. Until, at least,
+13 September 2023, Stack releases would aim to support the immediate
+predecessor, GHC 7.10.3 and `base-4.8.2.0` and `Cabal-1.22.5.0`.
 
 When a version of the Stack executable actually ceases to support a version of
 GHC and `Cabal`, that should be recorded in Stack's