docs: Update the example config

Issue #13

config.example.yaml

@@ -5,8 +5,9 @@
 #  "CacheEnabled":     "true",
 #  "CacheCompression": "true",
 #  "CacheDir":         "./run/cache",
-#  "X509Key":          "./run/key.pema",
+#  "X509Key":          "./run/key.pem",
-#  "X509Cert":         "./run/cert.pema",
+#  "X509Cert":         "./run/cert.pem",
 #  "CookieJar":        "./run/cookies.json",
+#  "CredentialsStore": "./run/credentials.json",
 #  "ServerAddress":    "[::0]"
 }