move clusters page to tips

also add a section on the front page highlighting major new features

doc/git-annex-extendcluster.mdwn

@@ -35,7 +35,7 @@ after adding the new gateway repository as a remote.
 [[git-annex-updatecluster]](1)
 [[git-annex-updateproxy]](1)
 
-<https://git-annex.branchable.com/clusters/>
+<https://git-annex.branchable.com/tips/clusters/>
 
 # AUTHOR
 

doc/git-annex-initcluster.mdwn

@@ -30,7 +30,7 @@ documentation of that command for details about configuring nodes.
 [[git-annex-preferred-content]](1)
 [[git-annex-updateproxy]](1)
 
-<https://git-annex.branchable.com/clusters/>
+<https://git-annex.branchable.com/tips/clusters/>
 
 # AUTHOR
 

doc/git-annex-updatecluster.mdwn

@@ -34,7 +34,7 @@ use [[git-annex-extendcluster]].
 [[git-annex-extendcluster]](1)
 [[git-annex-updateproxy]](1)
 
-<https://git-annex.branchable.com/clusters/>
+<https://git-annex.branchable.com/tips/clusters/>
 
 # AUTHOR
 

doc/links/key_concepts.mdwn

@@ -4,6 +4,10 @@
 * [[how_it_works]]
 * [[special_remotes]]
 * [[workflows|workflow]]
-* [[sync]]
 * [[preferred_content]]
-* [[clusters]]
+* [[sync]]
+
+### new features
+
+* [[tips/clusters]]
+* [[git-remote-annex|tips/storing_a_git_repository_on_any_special_remote]]