readme: point out that we require our ceph fork

Signed-off-by: Joao Eduardo Luis <[email protected]>

README.md

@@ -57,6 +57,15 @@ If one is new to Ceph development, the best way to find out how to build
 these sources is to refer to the
 [original documentation](https://docs.ceph.com/en/pacific/install/build-ceph/#id1).
 
+Because we are in a fast development effort at the moment, we have chosen to
+apply patches needed to make our endeavour work on our own fork of the Ceph
+repository. This allows us fiddle with the Ceph source while experimenting,
+without polluting the upstream Ceph repository. We do intend to upstream any
+patches that make sense though.
+
+That said, we have the `aquarist-labs/ceph` repository as a requirement for
+this project. We can't guarantee that our instructions, or the project as a
+whole, will work flawlessly with the original Ceph project from `ceph/ceph`.
 
 ### Running