CANN: GGML_CANN_ACL_GRAPH works only USE_ACL_GRAPH enabled (#16861)

The documentation should state that `GGML_CANN_ACL_GRAPH` is only effective if `USE_ACL_GRAPH` was enabled at compilation time.

diff --git a/docs/backend/CANN.md b/docs/backend/CANN.md
index e45fc7dd28f388de975147212295313c9697c226..37dcfaef9a84d22fe40336cece90afadd0bb3c68 100755 (executable)
--- a/docs/backend/CANN.md
+++ b/docs/backend/CANN.md
@@ -313,7 +313,12 @@ Converting the matmul weight format from ND to NZ to improve performance. Enable
 
 ### GGML_CANN_ACL_GRAPH
 
-Operators are executed using ACL graph execution, rather than in op-by-op (eager) mode. Enabled by default.
+Operators are executed using ACL graph execution, rather than in op-by-op (eager) mode. Enabled by default. This option is only effective if `USE_ACL_GRAPH` was enabled at compilation time. To enable it, recompile using:
+
+```sh
+cmake -B build -DGGML_CANN=on -DCMAKE_BUILD_TYPE=release -DUSE_ACL_GRAPH=ON
+cmake --build build --config release
+```
 
 ### GGML_CANN_GRAPH_CACHE_CAPACITY