Polish README Community section wording

[Danmushu]

Summary

• Align the English Community section with the Chinese README.
• Replace literal phrasing with natural, action-oriented technical English.
• Clarify the descriptions of Discussions, Issues, Contributing, and Ontology2SQL.

Testing

• Not run; documentation-only change.
• git diff --check passed.

Notes

• No functional changes.
• Existing links remain unchanged.

[WaylandYang]

Thanks, the first three lines read better and match the Chinese copy. One nit: please keep "method" on the Ontology2SQL line. The feature table above says "the method behind it", and the Chinese README says 方法, so "approach" makes the two inconsistent. Happy to merge once that's back.