dir watcher docs

docs/directorywatcher.md

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+# [Directory Watcher](https://github.com/Knox-AAU/PreProcessingLayer_EntityRecognitionAndLinking/blob/main/lib/DirectoryWatcher.py)
+The pipeline starts when a new file is placed in a watched folder by pipeline part A. The Directory Watcher's responsibility is to call a callback function when a new file is created in the watched folder.
+
+## Features
+- [watchdog](https://pypi.org/project/watchdog/) for file events
+- Async callback support
+- [Threading](https://docs.python.org/3/library/threading.html)
+
+## Overview
+
+The `DirectoryWatcher` provides a simple way to monitor a specified directory for file creation events and execute asynchronous callbacks in response. It utilizes the [watchdog](https://pypi.org/project/watchdog/) library for filesystem monitoring and integrates with [asyncio](https://docs.python.org/3/library/asyncio.html) for handling asynchronous tasks. Furthermore the `DirectoryWatcher` uses [threading](https://docs.python.org/3/library/threading.html).
+
+> **_NOTE:_**  [Threading](https://docs.python.org/3/library/threading.html) is used to avoid blocking the main thread's code from executing.
+
+
+## Example usage
+```python
+# Importing
+from lib.DirectoryWatcher import DirectoryWatcher
+
+dirPath = "some/path/to/a/directory"
+
+# Setup
+async def newFileCreated(file_path: str):
+    print("New file created in " + file_path)
+
+
+dirWatcher = DirectoryWatcher(
+    directory=dirPath, async_callback=newFileCreated
+)
+
+# A fast API event function running on startup
+@app.on_event("startup")
+async def startEvent():
+    dirWatcher.start_watching()
+
+# A fast API event function running on shutdown
+@app.on_event("shutdown")
+def shutdown_event():
+    dirWatcher.stop_watching()
+```
+
+> **_NOTE:_**  The fast API event functions are not needed to use the `Directory Watcher`
+
+
+## Methods
+```python
+def __init__(self, directory, async_callback):
+```
+### Parameters:
+- **directory** (str): A path to the directory you want to watch ie. `some/path/to/a/directory`
+- **async_callback** (function): An async callback function to be called when a new file is created in the **directory**. This function should accept a single parameter, which is the path of the created file.
+
+```python
+def start_watching(self) -> threading.Thread:
+```
+
+```python
+def stop_watching(self):
+```