bst2html doc's

Summary

bst2html refers to the CONTRIBUTING guild but the guild dose not refer back to it so if the information that it describes is in there it is hard to find, I could not find it.

doc/bst2html.py --help
Usage: bst2html.py [OPTIONS] DESCRIPTION

  Run a bst command and capture stdout/stderr in html

  This command normally takes a description yaml file, see the CONTRIBUTING
  file for information on it's format.

if the information is some were else then the doc string should be updated else could we make it easier to find the info in CONTRIBUTING

Other relevant information

• BuildStream version affected: current master: 49df3d75

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