Fix Grammar and Punctuation in Documentation

[Daulox92]

Changes:

1. docs/SPECIFICATION.md:

• A POST request to the /transfers endpoint can be made register, move or deregister a username.

• A POST request to the /transfers endpoint can be made to register, move or deregister a username.

Reason: Added missing "to" for proper infinitive phrase structure.

2. docs/OVERVIEW.md:

• Timestamps are unreliable, data isn't permanent and there are no mechanisms for private messaging.

• Timestamps are unreliable, data isn't permanent, and there are no mechanisms for private messaging.

Reason: Added serial comma for clarity in technical writing.

These changes improve documentation readability while maintaining technical accuracy.