doc: refine format

Author: zhouwg

README.md

@@ -258,7 +258,7 @@ end
 
 block:ggml
    ggml["GGML"]
-   style ggml fill:#3c3,color:#000,stroke:#000
+   style ggml     fill:#3c3,color:#000,stroke:#000
 
    ggml_cpu["ggml-cpu"]
    ggml_metal["ggml-metal"]
@@ -272,23 +272,23 @@ block:ggml
    ggml_nnpa["ggml-nnpa"]
    ggml_ane["ggml-ane"]
 
-   style ggml_cpu  fill:#888,color:#000,stroke:#000
-   style ggml_metal  fill:#888,color:#000,stroke:#000
-   style ggml_sycl  fill:#888,color:#000,stroke:#000
-   style ggml_cuda fill:#888,color:#000,stroke:#000
-   style ggml_hip fill:#888,color:#000,stroke:#000
-   style ggml_vulkan  fill:#888,color:#000,stroke:#000
-   style ggml_cann  fill:#888,color:#000,stroke:#000
-
-   style ggml_opencl fill:#cc3,color:#000,stroke:#000
-   style ggml_qnn fill:#cc3,color:#000,stroke:#000
-   style ggml_ane fill:#fff,color:#000,stroke:#f00,stroke-width:2,stroke-dasharray:5
-   style ggml_nnpa fill:#cc3,color:#000,stroke:#000
+   style ggml_cpu       fill:#888,color:#000,stroke:#000
+   style ggml_metal     fill:#888,color:#000,stroke:#000
+   style ggml_sycl      fill:#888,color:#000,stroke:#000
+   style ggml_cuda      fill:#888,color:#000,stroke:#000
+   style ggml_hip       fill:#888,color:#000,stroke:#000
+   style ggml_vulkan    fill:#888,color:#000,stroke:#000
+   style ggml_cann      fill:#888,color:#000,stroke:#000
+
+   style ggml_opencl    fill:#cc3,color:#000,stroke:#000
+   style ggml_qnn       fill:#cc3,color:#000,stroke:#000
+   style ggml_ane       fill:#fff,color:#000,stroke:#f00,stroke-width:2,stroke-dasharray:5
+   style ggml_nnpa      fill:#cc3,color:#000,stroke:#000
 end
 
 block:ggml_pal
    ggml_pal["GGML Platform Abstraction Layer"]
-   style ggml_pal fill:#c33,color:#000,stroke:#000
+   style ggml_pal       fill:#c33,color:#000,stroke:#000
 end
 
 
@@ -316,7 +316,7 @@ block:hardware_vendors
     ggml_cann   --> Huawei
     ggml_sycl   --> Intel
     ggml_opencl --> Qualcomm
-    ggml_qnn    -->Qualcomm
+    ggml_qnn    --> Qualcomm
     ggml_ane    --> Apple
     ggml_nnpa   --> IBM
 end