Add instructions for Trunk, add PGXN badge

[artemgavrilov]

[codecov[bot]]

Codecov Report

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

Project coverage is 84.56%. Comparing base (fdec44a) to head (cdc394b).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #473 +/- ## ======================================= Coverage 84.56% 84.56% ======================================= Files 3 3 Lines 1270 1270 Branches 196 196 ======================================= Hits 1074 1074 Misses 98 98 Partials 98 98 ```

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