Add action for document building

[wangnuannuan]

1. there is 1 job created in this action

• job to build HTML

Before create this action , we need to create a repo secret, because we need to publish the generated files to another repo https://github.com/foss-for-synopsys-dwc-arc-processors/foss-for-synopsys-dwc-arc-processors.github.io.

1. Generate a new Personal access tokens
2. Go to https://github.com/foss-for-synopsys-dwc-arc-processors/toolchain, Settings->Secrets->New repository secret, name the secret as ACTION_TOKEN, and then copy Personal access tokens you create before.

https://github.com/wangnuannuan/toolchain/actions

Signed-off-by: Jingru Wang [email protected]

[wangnuannuan]

Because we need use rst2pdf module, so the version of Sphinx should not newer than 4.*, there is an action https://github.com/ammaraskar/sphinx-action can be used, but it is based on on container shpinx-doc, an in this container, the version of Sphinx is 4.1.2.. https://github.com/sphinx-doc/docker/blob/master/base/Dockerfile#L15 So I think it's better to use ubuntu container, and then install Sphinx modules with pip

[kolerov]

It's already done in these accepted PRs:

1. https://github.com/foss-for-synopsys-dwc-arc-processors/toolchain/pull/508
2. https://github.com/foss-for-synopsys-dwc-arc-processors/toolchain/pull/516