Clarify MTMD markers and improve markdown

Author: 65a

tools/server/README.md

@@ -408,7 +408,8 @@ Multiple prompts are also supported. In this case, the completion result will be
   - Strings and sequences of tokens: `["string1", [12, 34, 56]]`
   - Mixed types: `[[12, 34, "string", 56, 78], [12, 34, 56], "string"]`
 
-`multimodal_data`: Optional. Should be an array of strings, containing base64 encoded multimodal data (e.g. images, audio). There must be an identical number of MTMD media markers in the raw prompt which act as placeholders for the data provided to this parameter. The multimodal data files will be substituted in order.
+
+`multimodal_data`: Optional. Should be an array of strings, containing base64 encoded multimodal data such as images and audio. There must be an identical number of MTMD media markers in the raw prompt which act as placeholders for the data provided to this parameter. The multimodal data files will be substituted in order. The marker string (e.g. `<__media__>`) can be found by calling `mtmd_default_marker()` defined in [the MTMD C API](https://github.com/ggml-org/llama.cpp/blob/5fd160bbd9d70b94b5b11b0001fd7f477005e4a0/tools/mtmd/mtmd.h#L87). 
 
 `temperature`: Adjust the randomness of the generated text. Default: `0.8`