[Python] Add source build guide for CentOS 6 (with devtoolset) and CentOS 7



**Reporter**: [Wes McKinney](https://issues.apache.org/jira/browse/ARROW-959) / @wesm

<sub>**Note**: *This issue was originally created as [ARROW-959](https://issues.apache.org/jira/browse/ARROW-959). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*</sub>