Basic usage documentation fix

[mattkhn]

Hi,

While attempting to reduce the time needed by malt to profile an application, I spotted a typo in the Basic usage documentation [here].(https://github.com/memtt/malt/blob/master/doc/source/start/basic-usage.rst#fast-profiling)

# Run fast without analysing the stacks
malt -o stacks:mode=none ./basic-example

should be fixed with

# Run fast without analysing the stacks
malt -o stack:mode=none ./basic-example

Best regards,
Matthieu.

[svalat]

Hi @mattkhn thanks for pointing the issue, this is fixed in branch develop.