update: clarify LLDB breakpoint behavior with Mojo JIT compilation

[Bakobiibizo]

This PR addresses issue #228 and clarifies breakpoint behavior in the debugging tutorial when using LLDB with Mojo programs. The current tutorial implies the breakpoint should resolve immediately, which can make the warning message look like an error when it shows the breakpoint being set . Which can be confusing for readers because it appears as though the breakpoint failed, even though it resolves automatically once the program begins execution and the module is compiled.

essentials.md

• Document that pending breakpoints are expected when debugging JIT-compiled Mojo programs
• Explain that LLDB registers the breakpoint but cannot bind it to an address until execution begins
• Clarify that the breakpoint resolves automatically after the program starts running

This was encountered while following the GPU Puzzles debugging section, where br set -n main initially reports the breakpoint as unresolved even though it resolves correctly once run is executed. It is documented in issue #228