[ docs ] Add lldb-server debugger guide file

- In order to attach debugger to android unittest, using lldb is quite useful.
- Add some guidelines to attach

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Signed-off-by: skykongkong8 <ss.kong@samsung.com>

diff --git a/docs/how-to-debug-on-remote-android.md b/docs/how-to-debug-on-remote-android.md
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+# Debugging remotely using lldb-server
+By following this tutorial, users can learn how to install and run a cross-compiled unittest executable with the lldb-server debugger attached.
+
+## Install lldb from ndk
+- This tutorial assumes that the user has already installed the NDK as a prerequisite. Follow [here](https://github.com/nnstreamer/nntrainer/blob/main/docs/how-to-run-example-android.md) if not installed.
+- Then you can get the lldb-server from the NDK. (Skip if already installed)
+
+1. On your terminal, find where your lldb at by:
+```bash
+find "$ANDROID_NDK/toolchains/llvm/prebuilt" -name lldb-server
+```
+2. Push your lldb to remote Android device 
+> Note : Path of ndk might differ
+```bash
+adb push "$ANDROID_NDK"/toolchains/llvm/prebuilt/linux-x86_64/lib64/clang/14.0.6/lib/linux/aarch64/* /data/local/tmp/{$YOUR_WORKING_DIRECTORY}
+```
+
+## Prepare debuggable executable
+
+### 1. Android build
+```bash
+cd ~/nntrainer
+./tools/package_android.sh
+cd ./test/jni
+ndk-build NDK_DEBUG=1;
+```
+
+### 2. Collect binaries
+You need *.so libraries and executables with debug_info, not stripped for lldb.
+Find and push executables by:
+```bash
+cd ~/nntrainer/test/obj/local/arm64-v8a
+adb push unittest_* /data/local/tmp/{$YOUR_WORKING_DIRECTORY}
+cd ~/nntrainer/builddir/obj/local/arm64-v8a
+adb push *.so /data/local/tmp/{$YOUR_WORKING_DIRECTORY}
+```
+
+## How to run
+
+### 1. Port forwarding
+Please forward the port in the terminal. You may choose any port number that is convenient for you.
+```bash
+adb forward tcp:5039 tcp:5039
+```
+### 2. Start lldb server on adb shell (on android remote host)
+1. On your terminal, connect to your device via adb shell
+```bash
+adb shell
+```
+2. On adb shell, activate your lldb-server.
+```adb
+/data/local/tmp/{$YOUR_WORKING_DIRECTORY}/lldb-server platform --listen '*:5039' --server
+```
+### 3. Start lldb from local host
+On your terminal, start lldb. Activated lldb-server will start to establish connection immediately.
+```bash
+lldb -o 'platform select remote-android' \
+-o 'platform connect connect://:5039' \
+-o 'platform shell cd /data/local/tmp/{$YOUR_WORKING_DIRECTORY}'
+```
+### 4. Platform workspace setting
+On your lldb shell, set your workspace.
+```lldb
+platform settings -w /data/local/tmp/{$YOUR_WORKING_DIRECTORY}
+```
+### 5. Formulate executable target
+On your lldb shell, set your target executable to debug
+```lldb
+target create {$YOUR_EXECUTABLE_BINARY_TO_DEBUG}
+```
+For example,
+```lldb
+target create unittest_layers
+```
+### 7. process launch with ld library path
+On your lldb shell, launch your process with LD_LIBRARY_PATH included
+This might take a while. Wait patiently after the execution...
+```lldb
+process launch --environment LD_LIBRARY_PATH=.
+```
+
+## Tips while debugging
+   1. set breakpoints
+      1. refer to [break point commands](https://lldb.llvm.org/use/map.html)
+   2. `continue` : if you want to inspect the next
+   3. `image lookup -va $pc` :  inspect current image