Update the checksums for the 3.0 release notes files.

Also mention the binaries existence in the top level file.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@75177 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775