Adding more info to the `chemical` pages

[Adafede]

Fixes # (issue number, if applicable)

Description

Please include a summary of the change, relevant motivation and context. If possible and applicable, include before and after screenshots and a URL where the changes can be seen.

Caveats

Please list anything which has been left out of this PR or which should be considered before this PR is accepted Check any of the following which apply:

• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update
  • [ ] I have made corresponding changes to the documentation
• [ ] This change requires new dependencies (please list)

If you make changes to the Python code

• [ ] My code passes the tox check, I can receive warnings about tests, documentation or both

Testing

Please describe the tests that you ran to verify your changes. Provide instructions, so we can reproduce. Please also list any relevant details for your test configuration.

• http://127.0.0.1:8100/chemical/Q302204
• http://127.0.0.1:8100/chemical/Q128896073

Checklist

• [x] I have commented my code, particularly in hard-to-understand areas
• [x] My changes generate no new warnings
• [x] I have not used code from external sources without attribution
• [x] I have considered accessibility in my implementation
• [x] There are no remaining debug statements (print, console.log, ...)

[Adafede]

Added

• biological processes in which the chemical is involved
• additional matrices in which the chemical is found that are not taxa, but natural products of taxa

@egonw