Add CI doc (#1253)

* Add CI doc

Author: ihnorton

ci/README.md

@@ -0,0 +1,44 @@
+# CI documentation
+
+TileDB-Py currently uses two CI services:
+  - GitHub actions for routine CI
+  - Azure Pipelines for release packaging
+
+## GitHub Actions
+
+<TODO>
+
+### Nightly Builds
+
+- <triggering setup>
+
+## Azure Pipelines
+
+AZP is configured in [azure-pipelines.yml](), which points to two pipeline files in `misc`:
+  - [misc/azure-ci.yml](): Legacy CI, to ensure that the release build continue to work.
+  - [misc/azure-release.yml](): release build system, which creates Python wheels for PyPI distribution.
+
+
+### Release builds
+
+AZP release builds
+
+### Service Connection
+
+In order to create issues after nightly build failure, the AZP nightly pipeline uses a service connection
+with authorization to post to GitHub.
+  - Configuration page: [https://dev.azure.com/TileDB-Inc/CI/_settings/adminservices](https://dev.azure.com/TileDB-Inc/CI/_settings/adminservices)
+  - Connection name: `TileDB-Py-Test`
+  - Setup, from services configuration page above:
+    - Create a new Personal Access token
+      - At present, the repo dispatch token must be linked to an individual user account.
+      - Visit: https://github.com/settings/tokens/new
+      - Create token with `public_repo` scope and 1 year expiration (maximum)
+    - Visit configuration page linked above
+      - Select `New Service Connection`
+      - Select `Generic`
+        - Server URL: `https://api.github.com/`
+        - Password/token: <GitHub personal access token created above>
+      - Disable access to all repositories (will require pipeline-specific authorization on first pipeline execution)
+    - Save the new connection. Note that the connection name must match the name specified for
+      `connectedServieName` in `misc/azure-release.yml`. Note that you