Add prettier RC file

This file is copied from openbmc-build-scripts:config/prettierrc.yaml,
which is the default for BMC CI. The presence of the RC file is so that
autoformat plugins/extensions will now if this project should be
formatted.

Change-Id: I31430dd26d7c2ddd2d46fa125e164d31b157982b
Signed-off-by: Zane Shelley <zshelle@us.ibm.com>
diff --git a/.prettierignore b/.prettierignore
new file mode 100644
index 0000000..796b96d
--- /dev/null
+++ b/.prettierignore
@@ -0,0 +1 @@
+/build