update the shim README.md and add two articles to introduce how to create and run confidential computing container

For demonstration purpose, the reference container images are
availbale. Currently, web application demos based on OpenJDK 11
and Golang are provided.
Signed-off-by: Jia Zhang <zhang.jia@linux.alibaba.com>

Signed-off-by: NYilin Li <YiLin.Li@linux.alibaba.com>

Signed-off-by: Jia Zhang <zhang.jia@linux.alibaba.com>

Signed-off-by: NYilin Li <YiLin.Li@linux.alibaba.com>

Signed-off-by: Jia Zhang <zhang.jia@linux.alibaba.com>

- Add docs/running_rune_with_occlum_bundle.md
- Remove docs/running_rune_with_docker.md
- Update skeleton README.md to add way to run rune with skeleton bundle
- Update README.md of inclavare-containers
- Add docs/running_rune_with_occlum.md
Signed-off-by: NYilin Li <YiLin.Li@linux.alibaba.com>

Signed-off-by: Jia Zhang <zhang.jia@linux.alibaba.com>

Signed-off-by: Jia Zhang <zhang.jia@linux.alibaba.com>

Refer to docs/rune_quick_start.md available in occlum github repository instead
of docs/running_occlum_with_rune.md in this repository.
Signed-off-by: NYilin Li <YiLin.Li@linux.alibaba.com>

Signed-off-by: Jia Zhang <zhang.jia@linux.alibaba.com>

Signed-off-by: NYilin Li <YiLin.Li@linux.alibaba.com>
Signed-off-by: Jia Zhang <zhang.jia@linux.alibaba.com>

inclavare-containers is a set of tools for running trusted
applications in containers with the hardware-assisted enclave
technology. Enclave, referred to as a protected execution
environment, prevents the untrusted entity from accessing the
sensitive and confidential assets in use.

Currently, inclavare-containers consists of two core components:
rune and enclave runtime.

rune is a CLI tool for spawning and running enclaves in containers
according to the OCI specification. The codebase of rune is
a fork of runc, so rune can be used as runc if enclave is not
configured or available.

Enclave runtime is the backend of rune, which is responsible
for loading and running applications inside enclaves. The
interface between rune and enclave runtime is Enclave Runtime PAL
API, which allows invoking enclave runtime through well-defined
functions. The software for confidential computing may benefit
from this interface to interact with OCI runtime.

Additionally, this commit includes additional information about the
use of inclavare-containers.
- Run sample enclave runtime skeleton with rune
- Run enclave runtime Occlum with rune

See README.md for more details.
Signed-off-by: Jia Zhang <zhang.jia@linux.alibaba.com>
Signed-off-by: NXiaozhe Wang <wangxiaozhe@linux.alibaba.com>
Signed-off-by: NYilin Li <YiLin.Li@linux.alibaba.com>