Add an official example that uses `SB()` without the context manager `with` block

[mdmintz]

Add an official example that uses SB() without the context manager with block.

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Multiple people have now asked about how to use the SB() context manager without the with block.
This is mentioned in the Python documentation, but not directly here, so I'll add an example for it.

This involves calling the built-in __enter__() and __exit__() methods to simulate the start and end of the with block.

Basic example of that:

from seleniumbase import SB

sb_context = SB()
sb = sb_context.__enter__()
sb.open("data:text/html,<h1>Test Page</h1>")
sb.highlight("h1", loops=8)
sb_context.__exit__(None, None, None)

That same example with the standard context manager with block looks like this:

from seleniumbase import SB

with SB() as sb:
    sb.open("data:text/html,<h1>Test Page</h1>")
    sb.highlight("h1", loops=8)

[mdmintz]

This was resolved in 4.41.3 - https://github.com/seleniumbase/SeleniumBase/releases/tag/v4.41.3