doc: Post 3.0.0-preview1 release doc updates

Post 3.0.0-preview1 release doc updates

Signed-off-by: Uma Praseeda <uma.praseeda@nordicsemi.no>

Author: umapraseeda

doc/nrf/releases_and_maturity/release_notes.rst

@@ -21,6 +21,7 @@ This page is included only in the latest documentation, because it might contain
    :caption: Subpages:
 
    releases/release-notes-changelog
+   releases/release-notes-3.0.0-preview1
    releases/release-notes-2.9.0-nRF54H20-1-rc2
    releases/release-notes-2.9.0
    releases/release-notes-2.8.0