v0.6.3

docs: restructure Spine-Runtime documentation (#1)

* docs: Move quickstart example to examples/quickstart

The quickstart sources and their two build workflows are embedded in the
README as fenced blocks, which cannot be configured or built in place.
Move them into `examples/quickstart` as a standalone CMake project with
its own README, and point the README quickstart section at it.

Signed-off-by: Yuting Nie <yuting.nie@spacemit.com>

* docs: Move programming model to docs/programming-model.md

The programming model section is reference material rather than
onboarding text. Move it into `docs/programming-model.md` together with
its Chinese translation, and leave a pointer in the README.

Signed-off-by: Yuting Nie <yuting.nie@spacemit.com>

* docs: Move multicore scheduling to docs/scheduling.md

The multicore scheduling model section, including the K3 scheduling and
resource-contention diagrams, is reference material rather than
onboarding text. Move it into `docs/scheduling.md` together with its
Chinese translation, and leave a pointer in the README.

Signed-off-by: Yuting Nie <yuting.nie@spacemit.com>

* docs: Move API overview to docs/api-reference.md

The API and feature overview section, covering the public C++ API
tables, status codes, the compiler-integration ABI and package
integration, is reference material rather than onboarding text. Move it
into `docs/api-reference.md` together with its Chinese translation, and
leave a pointer in the README.

Signed-off-by: Yuting Nie <yuting.nie@spacemit.com>

* docs: Move backend modes to docs/backends.md

The supported backend modes section is reference material rather than
onboarding text. Move it into `docs/backends.md` together with its
Chinese translation, and leave a pointer in the README.

Signed-off-by: Yuting Nie <yuting.nie@spacemit.com>

* docs: Simplify README into overview with pointers

With the quickstart and reference sections moved into `examples/` and
`docs/`, the README only needs to introduce SpineRuntime and route
readers. Slim it down to an overview with the key features, a
getting-started path and a documentation table, in both English and
Chinese.

Signed-off-by: Yuting Nie <yuting.nie@spacemit.com>

* docs: Add repo link

Signed-off-by: YutingNie <yuting.nie@spacemit.com>

* docs: clarify Bianbu package availability

Signed-off-by: YutingNie <yuting.nie@spacemit.com>

---------

Signed-off-by: Yuting Nie <yuting.nie@spacemit.com>
Signed-off-by: YutingNie <yuting.nie@spacemit.com>