docs: fix markdown check issues

- Removes `CODE_OF_CONDUCT.md` and `CONTRIBUTING.md` from osbuilder
directory.
- Fixes a reference from `image-builder/README.md` to
`rootfs-builder/README.md`
- Updates the main `README.md` making a reference to the local
`tools/osbuilder/README.md`

Signed-off-by: Salvador Fuentes <salvador.fuentes@intel.com>

README.md

@@ -128,7 +128,7 @@ as the component it tests).
 
 #### OS builder
 
-The [osbuilder](https://github.com/kata-containers/osbuilder) tool can create
+The [osbuilder](tools/osbuilder/README.md) tool can create
 a rootfs and a "mini O/S" image. This image is used by the hypervisor to setup
 the environment before switching to the workload.
 

tools/osbuilder/CODE_OF_CONDUCT.md

@@ -1,3 +0,0 @@
-## Kata Containers osbuilder Code of Conduct
-
-Kata Containers follows the [OpenStack Foundation Code of Conduct](https://www.openstack.org/legal/community-code-of-conduct/).

tools/osbuilder/CONTRIBUTING.md

@@ -1,5 +0,0 @@
-# Contributing
-
-## This repo is part of [Kata Containers](https://katacontainers.io)
-
-For details on how to contribute to the Kata Containers project, please see the main [contributing document](https://github.com/kata-containers/community/blob/master/CONTRIBUTING.md).

tools/osbuilder/image-builder/README.md

@@ -17,7 +17,7 @@ $ sudo ./image_builder.sh path/to/rootfs
 Where `path/to/rootfs` is the directory populated by `rootfs.sh`.
 
 > **Note**: If you are building an image from an Alpine rootfs, see
-> the important note [here](/rootfs-builder/README.md#rootfs-requirements).
+> the important note [here](/tools/osbuilder/rootfs-builder/README.md#rootfs-requirements).
 
 ## Further information