Update READMEs for painting/ and animation/ to be up to date with current dependencies.

packages/flutter/lib/animation/README.md

diff --git a/packages/flutter/lib/animation/README.md b/packages/flutter/lib/animation/README.md
index 3384c45..55f96ca 100644
--- a/packages/flutter/lib/animation/README.md
+++ b/packages/flutter/lib/animation/README.md
@@ -1,2 +1,2 @@
 This directory contains animation-related libraries that only depend
-on core Dart libraries and ../base/*.
+on core Dart libraries, the Newton Dart library, and ../base/*.

packages/flutter/lib/painting/README.md

diff --git a/packages/flutter/lib/painting/README.md b/packages/flutter/lib/painting/README.md
new file mode 100644
index 0000000..64967d7
--- /dev/null
+++ b/packages/flutter/lib/painting/README.md
@@ -0,0 +1,3 @@
+This directory contains painting-related libraries that only depend on
+core Dart libraries, ../base/*, and ../animation/*. Note that
+../animation/* depends on the Newton Dart library also.