Updated Continuous Integration (markdown)

Continuous-Integration.md

@@ -1,3 +1,23 @@
-This document discusses the Continuous Integration (CI) system for PyTorch.
+This document discusses the Continuous Integration (CI) system for PyTorch. Currently PyTorch utilizes Github Action, CircleCI and Jenkins CI for various different CI build/test configurations. We will discuss these related contents in the following sections:
+
+- [CI System Overview](#overview)
+  - [Github Action](#github-action)
+  - [CircleCI](#circleci)
+  - [Jenkins](#jenkins)
+- [CI Matrix](#ci-matrix)
+  - [Basic Configurations](#basic-configurations)
+  - [Variances](#configuration-variances)
+- [Entrypoint for CI](#ci-entry-point)
+  - [Build System](#ci-build)
+  - [Test System](#ci-test)
+  - [Binary Builds](#ci-binary)
+- [What is CI testing and When](#ci-what-and-when)
+  - [CI workflow on PR](#ci-on-pr)
+  - [CI workflow on master commits](#ci-on-master-commits)
+- [Customize CI behavior on PR](#customize-ci-on-pr)
+- [Other Topics](#other-topics)
+  - [What is the base commit used in CI for your PR?](#which-commit-is-used-in-ci)
+  - [CI failure tips on PR](#ci-failure-tips)
+
+
 
-TBA