Fix use of pem_read_buffer() in PK, DHM and X509
diff --git a/include/mbedtls/x509_crt.h b/include/mbedtls/x509_crt.h
index e184dee..aced7eb 100644
--- a/include/mbedtls/x509_crt.h
+++ b/include/mbedtls/x509_crt.h
@@ -141,8 +141,9 @@
* correctly, the first error is returned.
*
* \param chain points to the start of the chain
- * \param buf buffer holding the certificate data
+ * \param buf buffer holding the certificate data in PEM or DER format
* \param buflen size of the buffer
+ * (including the terminating null byte for PEM data)
*
* \return 0 if all certificates parsed successfully, a positive number
* if partly successful or a specific X509 or PEM error code