Resolve "Update developing plugin documentation"

docs/examples/computational_data/h5md_expl.md

docs/examples/computational_data/h5md_howto.md

docs/examples/computational_data/h5md_ref.md

docs/examples/computational_data/metainfo.md

docs/examples/computational_data/parser_plugins.md

docs/examples/computational_data/schema_plugins.md

docs/examples/computational_data/uploading.md

docs/examples/overview.md

docs/explanation/basics.md

docs/explanation/data.md

docs/explanation/processing.md

docs/howto/customization/base_sections.md

docs/howto/customization/basics.md

docs/howto/customization/elns.md

docs/howto/customization/normalizers.md

docs/howto/customization/parsers.md

docs/howto/customization/plugins.md

docs/howto/customization/schemas.md

docs/howto/customization/tabular.md

docs/howto/customization/units.md