Support wenet x86 cmake build being a sub-project (wenet-e2e#637)

* [runtime] support x86 cmake build wenet being a sub-project

* [runtime] export x86 cmake build openfst directory variables

[doc] update aishell2 u2++ transformer results (wenet-e2e#477)

* [doc] update aishell2 u2++ transformer results

* Update train_u2++_transformer.yaml

Co-authored-by: Binbin Zhang <811364747@qq.com>

Merge pull request wenet-e2e#418 from wenet-e2e/robin1001-readme

[doc] add essen acknowledgement

[doc] add new s0 aishell non-streaming result (wenet-e2e#143) (wenet-…

…e2e#144)

Co-authored-by: Di Wu <1176705630@qq.com>