This pull request adds a new tutorial under the "Learn the Basics" section for Java, focused on string manipulation.

The tutorial introduces common string operations such as concatenation, character access, searching substrings, substring extraction, and transformations (e.g. trim, toUpperCase). It includes a hands-on exercise that requires the user to manually reverse a string without using StringBuilder.reverse().

The tutorial follows the required structure:

• Explanation section
• Exercise instructions
• Starter code (Tutorial Code)
• Expected Output
• Solution

A link to the tutorial has also been added to the relevant Welcome.md file.

This should help users deepen their understanding of how to work with strings in Java from an early stage in the learning path.