[refactor] Direct reference for existing project docs

[zheliuyu]

Motivation

Related issue: #95

The goal of this refactoring is to reduce the maintenance cost of the documentation.

The specific principle is: if an open-source project provides comprehensive NPU usage documentation, Ascend/docs should directly link to and stay synchronized with this documentation.

Using the verl project as an example, I will explain how to implement this.

Method

Here, the verl project is used for demonstration.

• Use the git submodule to add the subproject to Ascend/docs. The benefits include:
  • Preventing Ascend/docs from becoming bloated by including entire projects.
  • Making updates extremely simple.
• Create an index.rst file in the sources/verl folder to serve as the table of contents for the verl project documentation. This allows users to control the scope of the documentation displayed. In other words, if users do not wish to display all of verl's documentation in Ascend/docs, they can manage this via the index.rst file.
• Add a series of operations to the Makefile:
  • Download verl's submodules before executing make html.
  • Copy verl's documentation files to the build directory. Using the VeOmni project as an example, I have added a warning prompt that triggers if the directory is empty.
  • A crucial step: clean up the submodules.

[zheliuyu]

Local Testing

[zheliuyu]

@fffrog @noemotiovon @lowdy1 Regarding the refactoring discussed in the previous issue, I plan to use this approach. Please review this pr. Thanks.