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.

Signed-off-by: Zane Shelley <zshelle@us.ibm.com>
Change-Id: Ief6e8f32f36eadc9e5b9d16bd41bdcc35a128d65
diff --git a/.prettierignore b/.prettierignore
new file mode 100644
index 0000000..796b96d
--- /dev/null
+++ b/.prettierignore
@@ -0,0 +1 @@
+/build