doc(Readme):modify the install method of c library

[ShannonDing]

What is the purpose of the change

modify the install method of c library

Brief changelog

download package from apache site

Verifying this change

see the introduction page

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• Make sure there is a Github issue filed for the change (usually before you start working on it). Trivial changes like typos do not require a Github issue. Your pull request should address just this issue, without pulling in other changes - one PR resolves one issue.
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