contributing: snakeviz replaces pyflame+flamegraph

Replace the instructions for pyflame+flamegraph with simpler ones for snakeviz. For our general use-case this seems to be easier and better. Usage of this tool was demonstrated at the 2019 BuildStream Gathering in January by Daniel Silverstone, when presenting the aggregate results of profiling on many target environments.

Here is the relevant mailing list thread:

"Profiling before the gathering" https://mail.gnome.org/archives/buildstream-list/2019-January/msg00057.html 1b5a49d2

approved this merge request

Looks good to me.

Looks good to me too

added 13 commits

• 1b5a49d2...e61f4713 - 12 commits from branch master
• 71e83835 - contributing: snakeviz replaces pyflame+flamegraph

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approved this merge request

enabled an automatic merge when the pipeline for 71e83835 succeeds

canceled the automatic merge

added 17 commits

• 71e83835...c07cc967 - 16 commits from branch master
• 9e3d3e05 - contributing: snakeviz replaces pyflame+flamegraph

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enabled an automatic merge when the pipeline for 9e3d3e05 succeeds

merged

mentioned in commit bb6a692d