message: Updating info on key templates in C++-HOWTO.
diff: @@ -218,8 +218,12 @@ directly in C++ code, one can use
  // use the keyset...
  ```
  -where `key_template` can be initialized with one of pre-generated templates from
  -[examples/keytemplates](https://github.com/google/tink/tree/master/examples/keytemplates)-folder.
  +where `key_template` can be obtain from util classes corresponding to Tink primitives, e.g.
  +[MacKeyTemplates](https://github.com/google/tink/blob/master/cc/mac/mac_key_templates.h),
  +[AeadKeyTemplates](https://github.com/google/tink/blob/master/cc/aead/aead_key_templates.h),
  +or
  +[HybridKeyTemplates](https://github.com/google/tink/blob/master/cc/hybrid/hybrid_key_templates.h).
  +
  ## Loading Existing Keysets
  