Add README.md

Signed-off-by: Adrien Gallouët <angt@huggingface.co>

backends/llamacpp/README.md

@@ -0,0 +1,24 @@
+# Llamacpp backend
+
+If all your dependencies are installed at the system level, running
+cargo build should be sufficient. However, if you want to experiment
+with different versions of llama.cpp, some additional setup is required.
+
+## Install llama.cpp
+
+    LLAMACPP_PREFIX=$(pwd)/llama.cpp.out
+
+    git clone https://github.com/ggerganov/llama.cpp
+    cd llama.cpp
+    cmake -B build \
+        -DCMAKE_INSTALL_PREFIX="$LLAMACPP_PREFIX" \
+        -DLLAMA_BUILD_COMMON=OFF \
+        -DLLAMA_BUILD_TESTS=OFF \
+        -DLLAMA_BUILD_EXAMPLES=OFF \
+        -DLLAMA_BUILD_SERVER=OFF
+    cmake --build build --config Release -j
+    cmake --install build
+
+## Build TGI
+
+    PKG_CONFIG_PATH="$LLAMACPP_PREFIX/lib/pkgconfig" cargo build