Document how imports work

As noted in https://github.com/bytecodealliance/ComponentizeJS/issues/88, it is not obvious how imports work. While I understand the hesitation to document this extensively as things are likely to change in the future, it makes it very hard for new comers to ComponentizeJS to use the tool if there is absolutely no documentation about how to call imports.

首先查看 issue #88 以及 ComponentizeJS 当前的 import 行为。通过一个具体的使用示例，记录用户如何调用 imports；当新贡献者无需未记录的上下文即可按照文档中的流程操作时，这项工作就完成了。

由索引模型根据 Issue 内容生成。