Fix up examples in src/schema/README.md to not use outdated schema paths

[yarikoptic]

I also developed a script to catch those no longer valid paths used. I think it is worth adding it on CI

• [x] find where in CI we produce that json dump of the schema, and add there running this script to ensure that all paths in README.md are valid
• (maybe elsewhere) decide if we should not choose simpler example or may be make it fuller (give example of secondary dereference)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 87.93%. Comparing base (327bece) to head (1c0edcd).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1698 +/- ## ======================================= Coverage 87.93% 87.93% ======================================= Files 16 16 Lines 1351 1351 ======================================= Hits 1188 1188 Misses 163 163 ```

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[yarikoptic]

I found where schema.org is produced -- in RTD, but there in env there is no jq so RTD succeeds but log says

tools/no-bad-schema-paths.sh: line 19: jq: command not found
meta.context.context: not reachable
tools/no-bad-schema-paths.sh: line 19: jq: command not found
objects.columns: not reachable
tools/no-bad-schema-paths.sh: line 19: jq: command not found
objects.common_principles: not reachable
tools/no-bad-schema-paths.sh: line 19: jq: command not found

moreover -- RTD succeeds! so that would not be appropriate place. we need to do it in another CI

[yarikoptic]

yeay -- it worked, removing TEMP commit: