feat(openthread): helper functions documentation

Create helper_functions.md for ESP32 Arduino OpenThread API

Author: SuGlider

libraries/OpenThread/helper_functions.md

@@ -0,0 +1,58 @@
+# OpenThread Helper Functions and Types
+
+The following helper functions and types are designed to simplify writing Arduino sketches for OpenThread. They provide useful utilities for managing OpenThread stack behavior and interacting with the Thread network.
+
+## Enumerated Type: `ot_device_role_t`
+
+This enumeration defines the possible roles of a Thread device within the network:
+
+- `OT_ROLE_DISABLED`: The Thread stack is disabled.
+- `OT_ROLE_DETACHED`: The device is not currently participating in a Thread network/partition.
+- `OT_ROLE_CHILD`: The device operates as a Thread Child.
+- `OT_ROLE_ROUTER`: The device operates as a Thread Router.
+- `OT_ROLE_LEADER`: The device operates as a Thread Leader.
+
+## Struct: `ot_cmd_return_t`
+
+This structure represents the return status of an OpenThread CLI command:
+
+- `errorCode`: An integer representing the error code (if any).
+- `errorMessage`: A string containing an error message (if applicable).
+
+## Function: `otGetDeviceRole()`
+
+- Returns the current role of the device as an `ot_device_role_t` value.
+
+## Function: `otGetStringDeviceRole()`
+
+- Returns a human-readable string representation of the device role (e.g., "Child," "Router," etc.).
+
+## Function: `otGetRespCmd(const char* cmd, char* resp = NULL, uint32_t respTimeout = 5000)`
+
+- Executes an OpenThread CLI command and retrieves the response.
+- Parameters:
+  - `cmd`: The OpenThread CLI command to execute.
+  - `resp`: Optional buffer to store the response (if provided).
+  - `respTimeout`: Timeout (in milliseconds) for waiting for the response.
+
+## Function: `otExecCommand(const char* cmd, const char* arg, ot_cmd_return_t* returnCode = NULL)`
+
+- Executes an OpenThread CLI command with an argument.
+- Parameters:
+  - `cmd`: The OpenThread CLI command to execute.
+  - `arg`: The argument for the command.
+  - `returnCode`: Optional pointer to an `ot_cmd_return_t` structure to store the return status.
+
+## Function: `otPrintRespCLI(const char* cmd, Stream& output, uint32_t respTimeout)`
+
+- Executes an OpenThread CLI command and prints the response to the specified output stream.
+- Parameters:
+  - `cmd`: The OpenThread CLI command to execute.
+  - `output`: The output stream (e.g., Serial) to print the response.
+  - `respTimeout`: Timeout (in milliseconds) for waiting for the response.
+
+## Function: `otPrintNetworkInformation(Stream& output)`
+
+- Prints information about the current Thread network to the specified output stream.
+- Parameters:
+  - `output`: The output stream (e.g., Serial) to print the network information.