Update the release notes and checksums for 3.0.1 release.

Also add an explicit notice about needing to compile the library even after
downloading the installer.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@76716 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775