Add interface documentation for the netfs helper library. Signed-off-by: David Howells <dhowells@redhat.com> cc: linux-mm@kvack.org cc: linux-cachefs@redhat.com cc: linux-afs@lists.infradead.org cc: linux-nfs@vger.kernel.org cc: linux-cifs@vger.kernel.org cc: ceph-devel@vger.kernel.org cc: v9fs-developer@lists.sourceforge.net cc: linux-fsdevel@vger.kernel.org Link: https://lore.kernel.org/r/161539533275.286939.6246011228676840978.stgit@warthog.procyon.org.uk/ # v4 Link: https://lore.kernel.org/r/161653791767.2770958.2012814194145060913.stgit@warthog.procyon.org.uk/ # v5 Link: https://lore.kernel.org/r/161789072591.6155.9448294406920216219.stgit@warthog.procyon.org.uk/ # v6
