Updated docs links, removed docs folder

[andogro]

GitHub keywords to close any associated issues

Motivation

Docs location has been updated to https://docs.blockscout.com/

Changelog

Enhancements

• updated doc links
• removed docs folder with redundant information

Bug Fixes

Things you changed that fix bugs. If a fixes a bug, but in so doing adds a new requirement, removes code, or requires a database reset and reindex, the breaking part of the change should be added to Incompatible Changes below also.

Incompatible Changes

Things you broke while doing Enhancements and Bug Fixes. Breaking changes include (1) adding new requirements and (2) removing code. Renaming counts as (2) because a rename is a removal followed by an add.

Upgrading

If you have any Incompatible Changes in the above Changelog, outline how users of prior versions can upgrade once this PR lands or when reviewers are testing locally. A common upgrading step is "Database reset and re-index required".

Checklist for your PR

• I added an entry to CHANGELOG.md with this PR
• If I added new functionality, I added tests covering it.
• If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.
• I checked whether I should update the docs and did so if necessary
• If I added/changed/removed ENV var, I should update the list of env vars in https://github.com/poanetwork/blockscout/blob/master/docs/env-variables.md to reflect changes in the table here https://poanetwork.github.io/blockscout/#/env-variables?id=blockscout-env-variables. I've set master in the Version column.
• If I add new indices into DB, I checked, that they don't redundant with PGHero or other tools