Add mTLS instructions

Change-Id: I4ac2896fa8d46418dbb08df9d9c08466fb51fdad
diff --git a/.gitignore b/.gitignore
index e781b44..1d8baba 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,3 +3,7 @@
 
 ipxe
 out/*
+
+# ignore crypto
+*.key
+*.pem