docs: Improve Hexagon backend README for Android deployment and commands

This commit refines the  by:

-   Adding a step to explicitly create the  directory on the Android device using  before pushing GGUF dels.
This ensures the target directory exists and prevents potential  failures.
-   Correcting the example  command by properly escaping the double quotes around the prompt string (). This ensures the command is correctly interpreted when executed in a shell environment.

These changes enhance the clarity and correctness of the instructions for deploying and running  on Snapdragon-based Android devices.

Author: xiukeding

docs/backend/snapdragon/README.md

@@ -109,6 +109,7 @@ At this point, you should also install some models:
 ...
 2025-10-11 12:04:52 (10.7 MB/s) - ‘Llama-3.2-1B-Instruct-Q4_0.gguf’ saved [773025920/773025920]
 
+~/src/llama.cpp$ adb shell mkdir -p /data/local/tmp/gguf
 ~/src/llama.cpp$ adb push Llama-3.2-1B-Instruct-Q4_0.gguf /data/local/tmp/gguf
 Llama-3.2-1B-Instruct-Q4_0.gguf: 1 file pushed, 0 skipped. 38.3 MB/s (773025920 bytes in 19.250s)
 ```
@@ -132,7 +133,7 @@ Here are some examples of running various llama.cpp tools via ADB.
 Simple question for Llama-3.2-1B
 
 ```
-~/src/llama.cpp$ M=Llama-3.2-1B-Instruct-Q4_0.gguf D=HTP0 ./scripts/snapdragon/adb/run-completion.sh -p "what is the most popular cookie in the world?"
+~/src/llama.cpp$ M=Llama-3.2-1B-Instruct-Q4_0.gguf D=HTP0 ./scripts/snapdragon/adb/run-completion.sh -p \"what is the most popular cookie in the world?\"
 ...
 ggml-hex: Hexagon backend (experimental) : allocating new registry : ndev 1
 ggml-hex: Hexagon Arch version v79