docs: add notes on serialization and file permission handling in Java

WHAT:
- Documented core concepts of object serialization and deserialization.
- Added explanation of the `Serializable` interface and behavior of `transient` and `static` fields.
- Summarized file permission methods available in the `File` class (`canRead`, `canWrite`, `canExecute`).
- Included example usage for checking and modifying file permissions.

WHY:
- Serialization is essential for persisting and transmitting objects (e.g., saving to files, sending over a network).
- File permission methods are critical for secure file handling and preventing unauthorized access.
- Developers need a concise reference for these common Java I/O practices.

KEY POINTS:
- Serialization:
  - Converts an object into a byte stream.
  - Deserialization reconstructs the object from the stream.
  - `transient` fields are skipped, `static` fields are not serialized.
- File Permissions:
  - `canRead()`, `canWrite()`, `canExecute()` → check existing permissions.
  - `setReadable()`, `setWritable()`, `setExecutable()` → modify permissions.
  - Behavior is OS-dependent and subject to Java Security Manager restrictions.

REAL-WORLD USE CASES:
- Serialization: Storing user sessions, caching objects, or transmitting data between distributed systems.
- File Permissions: Enforcing read-only configuration files, restricting log file edits, or controlling executable scripts.

NOTES:
- Always ensure serialVersionUID is defined in Serializable classes for version consistency.
- Permission methods may succeed or fail depending on the OS-level policies, not just Java code.

Signed-off-by: https://github.com/Someshdiwan <[email protected]>

Author: Someshdiwan

Section23JavaIOStreams/Serialisation Storing Data in a File/src/Serialisation.txt

@@ -11,13 +11,14 @@ The method canRead() of the File class is used to check if a file is readable.
 This method returns a boolean value indicating whether the application can read the file denoted by the File object.
 
 Key points about file permissions in Java:
+
 1. canRead(): Checks if the file is readable.
 2. canWrite(): Checks if the file is writable.
 3. canExecute(): Checks if the file is executable.
 4. setReadable(), setWritable(), setExecutable(): Methods to change file permissions.
 
 Example usage:
-```java
+
 File file = new File("example.txt");
 
 if (file.canRead()) {
@@ -35,10 +36,9 @@ if (file.canWrite()) {
 // Change permissions
 file.setWritable(true);
 file.setReadable(true, false); // true for all users, false for owner only
-```
 
 It's important to note that these methods work within the constraints of the underlying operating system
 and the Java Security Manager.
 
 The actual ability to read, write, or execute a file may depend on factors beyond just the file permissions,
-such as overall system security policies.
+such as overall system security policies.