Create presubmit.yaml which configures CI (#983)

Bazel runs a community CI server that has a bunch of free resources for
testing projects that opt into Bazel. This configures that resource.

.bazelci/presubmit.yml

@@ -0,0 +1,42 @@
+---
+platforms:
+  ubuntu1804:
+    build_flags:
+    - "--build_tag_filters=-nolinux"
+    build_targets:
+    - "..."
+    test_flags:
+    - "--features=race"
+    - "--test_tag_filters=-nolinux"
+    test_targets:
+    - "..."
+  ubuntu1604:
+    build_flags:
+    - "--build_tag_filters=-nolinux"
+    build_targets:
+    - "..."
+    test_flags:
+    - "--features=race"
+    - "--test_tag_filters=-nolinux"
+    test_targets:
+    - "..."
+  macos:
+    build_flags:
+    - "--build_tag_filters=-nomacos"
+    build_targets:
+    - "..."
+    test_flags:
+    - "--features=race"
+    - "--test_tag_filters=-nomacos"
+    test_targets:
+    - "..."
+  windows:
+    build_flags:
+    - "--build_tag_filters=-nowindows"
+    build_targets:
+    - "..."
+    test_flags:
+    - "--test_tag_filters=-nowindows"
+    - "--experimental_enable_runfiles"
+    test_targets:
+    - "..."