Enable clang-tidy

Copy in the .clang-tidy from docs/style/cpp.

Change-Id: I944709835562b6599ebfaa5e3e851aa3e48d6630
Signed-off-by: Matt Spinler <spinler@us.ibm.com>
diff --git a/.clang-tidy b/.clang-tidy
new file mode 100644
index 0000000..8b0c596
--- /dev/null
+++ b/.clang-tidy
@@ -0,0 +1,8 @@
+Checks: '-*,
+    bugprone-unchecked-optional-access,
+    modernize-use-nullptr
+    '
+
+HeaderFilterRegex: (?!^subprojects).*
+
+WarningsAsErrors: '*'