Note on emitting assembly

This is a small thing but I spent quite some time in the docs looking for how to get the machine assembly (because I would like to check for specific instructions) before remembering that Numba can do it. Poking around in Numba revealed the API, I saw that a simple modification of the llvmlite examples,
```python
asm = str(target_machine.emit_assembly(mod))
```
was enough. It could be nice to mention that or leave this issue here so others can find it if they look.

Start by locating the llvmlite examples and checking how target_machine and mod are introduced. Document that target_machine.emit_assembly(mod), converted to a string, provides machine assembly for inspecting instructions; done when the relevant docs mention this API.

Written by the indexing model from the issue text.