Sync from upstream llama.cpp repository

examples/passkey/README.md

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+# llama.cpp/example/passkey
+
+A passkey retrieval task is an evaluation method used to measure a language
+models ability to recall information from long contexts.
+
+See the following PRs for more info:
+
+- https://github.com/ggml-org/llama.cpp/pull/3856
+- https://github.com/ggml-org/llama.cpp/pull/4810
+
+### Usage
+
+```bash
+llama-passkey -m ./models/llama-7b-v2/ggml-model-f16.gguf --junk 250
+```