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

- Update deb to version 0.3.0
- Update rpm to version 0.3.0
Signed-off-by: Nshirong <shirong@linux.alibaba.com>

Base64 encode the signatrue when sending signature body from server and base64 decode signature when retriving signature  bodyfrom client

This rule enables building package useable for the running system.
Signed-off-by: Nshirong <shirong@linux.alibaba.com>

Signed-off-by: Nshirong <shirong@linux.alibaba.com>

1. Copy rpm package in temporary directory to top directory
2. Remove temporary directory
Signed-off-by: Nshirong <shirong@linux.alibaba.com>

- Add global `make rpm` for building rpms of rune and shim.
- Add rpm specs at rune/dist/centos and shim/dist/centos.
Signed-off-by: NYilin Li <YiLin.Li@linux.alibaba.com>
Signed-off-by: NChunmei Xu <xuchunmei@linux.alibaba.com>
Signed-off-by: NShirong Hao <shirong@linux.alibaba.com>
Signed-off-by: NZhiguang Jia <Zhiguang.Jia@linux.alibaba.com>

provide the enviorment variables for occlum configuration files and generate enclave configuration files from Occlum.json