Update README.md

[crprashant]

Summary

Adds a new "Using AGE with Non-Autocommit Clients (psycopg, JDBC, etc.)" section to the main README.md, documenting how PostgreSQL transaction semantics apply to AGE's DDL-like functions (create_graph, create_vlabel, create_elabel, drop_graph, etc.).

This is the "acceptable fallback" resolution proposed in #2195.

Refs #2195

Why

Users of non-autocommit clients (most commonly psycopg v3, also JDBC with autoCommit=false) report that graphs created via SELECT create_graph(...) appear to succeed but are not visible from new connections. The root cause is standard PostgreSQL behavior, not an AGE bug:

1. LOAD 'age' and SET search_path = ... are session-local and don't need a commit.
2. create_graph(...) and similar calls write to ag_catalog (and create schemas/tables). Those writes follow normal transactional visibility rules.
3. In psycopg v3, the very first statement (LOAD 'age') implicitly opens an outer transaction. A later with conn.transaction(): block then runs as a savepoint inside that outer transaction, not as a new top-level transaction. Releasing a savepoint is not a commit — so the create_graph write never becomes visible to other sessions until the outer transaction is explicitly committed (or the connection is closed on a clean commit path).

Since making create_graph bypass transactional visibility would violate ACID, the right fix is to document the requirement clearly, which is what this PR does.

What this PR adds

A new section in README.md (placed between Post Installation and Quick Start) containing:

• A table showing which AGE statements are session-local vs. transactional catalog writes.
• An explanation of the psycopg "savepoint gotcha" (with conn.transaction(): inside an already-open outer transaction).
• A broken psycopg v3 example reproducing the behavior reported in AGE extension requires explicit commit after LOAD/SET for proper initialization in non-autocommit clients #2195.
• Two working psycopg v3 fixes:
  • Explicit conn.commit() after LOAD / SET search_path.
  • psycopg.connect(..., autocommit=True).
• A short JDBC note covering both setAutoCommit(true) and explicit commit() after DDL-like calls.
• A one-line rule of thumb and a link back to AGE extension requires explicit commit after LOAD/SET for proper initialization in non-autocommit clients #2195.

What this PR does not do

• No code changes — documentation only.
• Does not modify drivers/python/README.md or any driver docs (the main README.md is the most discoverable place; happy to mirror a shortened version into a driver README if maintainers prefer).
• Does not change AGE's actual transactional behavior.

Testing

N/A — markdown-only. Rendered the section locally to confirm headings, code fences, and the table display correctly on GitHub.

Checklist

• Documentation-only change
• References the original issue (AGE extension requires explicit commit after LOAD/SET for proper initialization in non-autocommit clients #2195)
• No breaking changes
• No code or schema changes