Update SHA1 sums of 3.0.0-rc2 binaries.

Also mention the availability of two different architectures.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@75090 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Fix RC2 description in the announcement.

It's second, not first.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@75091 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775