Add aarch64 ci badge (pytorch#39698)

Summary:
This PR added a third-party aarch64 CI badge. It's CPU only currently for building pytorch master branch on python3.6 and Ubuntu 18.04. This CI is provided by OpenLab[1]

The build job runs once everyday at UTC0000

You can preview the badge here[2]

The build failed because of a known issue: pytorch#33124

More python version and GPU support will be added in the future.

This fixes pytorch#39558.

1: https://openlabtesting.org/
2: https://github.com/wangxiyuan/pytorch/tree/add_aarch64_ci_badge
Pull Request resolved: pytorch#39698

Differential Revision: D21960607

Pulled By: ezyang

fbshipit-source-id: 15d5c06e455ed1b5cf69c3b33906c098cb539f87

README.md

@@ -27,6 +27,7 @@ You can reuse your favorite Python packages such as NumPy, SciPy and Cython to e
 | Windows CPU / GPU | <center>—</center> | [![Build Status](https://ci.pytorch.org/jenkins/job/pytorch-builds/job/pytorch-win-ws2016-cuda9-cudnn7-py3-trigger/badge/icon)](https://ci.pytorch.org/jenkins/job/pytorch-builds/job/pytorch-win-ws2016-cuda9-cudnn7-py3-trigger/) |  <center>—</center> |
 | Linux (ppc64le) CPU | <center>—</center> | [![Build Status](https://powerci.osuosl.org/job/pytorch-master-nightly-py3-linux-ppc64le/badge/icon)](https://powerci.osuosl.org/job/pytorch-master-nightly-py3-linux-ppc64le/) | <center>—</center> |
 | Linux (ppc64le) GPU | <center>—</center> | [![Build Status](https://powerci.osuosl.org/job/pytorch-master-nightly-py3-linux-ppc64le-gpu/badge/icon)](https://powerci.osuosl.org/job/pytorch-master-nightly-py3-linux-ppc64le-gpu/) | <center>—</center> |
+| Linux (aarch64) CPU | [![Build Status](http://openlabtesting.org:15000/badge?project=pytorch%2Fpytorch&job_name=pytorch-arm64-build-daily-master)](https://status.openlabtesting.org/builds/builds?project=pytorch%2Fpytorch&job_name=pytorch-arm64-build-daily-master) | <center>—</center> | <center>—</center> |
 
 See also the [ci.pytorch.org HUD](https://ezyang.github.io/pytorch-ci-hud/build/pytorch-master).