Enable tls credential shell

Add a comment about switching between DER and PEM certs for
Memfault.

prj.conf

@@ -41,9 +41,13 @@ CONFIG_NET_L2_WIFI_SHELL=y
 CONFIG_MEMFAULT=y
 CONFIG_MEMFAULT_LOGGING_ENABLE=y
 CONFIG_MEMFAULT_HTTP_ENABLE=y
-CONFIG_MEMFAULT_TLS_CERTS_USE_DER=y
 CONFIG_MEMFAULT_HTTP_PERIODIC_UPLOAD=y
 
+# Using the DER format certs saves code and memory. To use PEM instead, swap
+# the comments on the following two lines.
+CONFIG_MEMFAULT_TLS_CERTS_USE_DER=y
+# CONFIG_MBEDTLS_PEM_CERTIFICATE_FORMAT=y
+
 # Additional network configuration for Memfault features
 CONFIG_DNS_RESOLVER=y
 CONFIG_NET_SOCKETS=y
@@ -60,6 +64,9 @@ CONFIG_MBEDTLS_SSL_MAX_CONTENT_LEN=4096
 CONFIG_MBEDTLS_MEMORY_DEBUG=y
 CONFIG_MBEDTLS_SHELL=y
 
+CONFIG_BASE64=y
+CONFIG_TLS_CREDENTIALS_SHELL=y
+
 # More verbose Memfault component logs
 CONFIG_MEMFAULT_LOG_LEVEL_DBG=y