Use a concrete specifier example in the upper-bound ask

Author: maxisbey

README.v2.md

@@ -19,7 +19,7 @@
 >
 > v2 is a major rework of the SDK, both to support the [2026-07-28 MCP specification release](https://blog.modelcontextprotocol.io/posts/2026-07-28-release-candidate/) and to fix long-standing architectural issues. See the [migration guide](https://github.com/modelcontextprotocol/python-sdk/blob/main/docs/migration.md) for what's changed. We're targeting a beta on 2026-06-30 and a stable v2 on 2026-07-27, alongside the spec release. Before stable, we plan to add a significant set of backwards compatibility shims so the final upgrade is much smaller than today's diff.
 >
-> **v1.x is the only stable release line and remains recommended for production.** It is in maintenance mode and continues to receive critical bug fixes and security patches. Installers never select a pre-release unless you opt in (for example `pip install mcp==2.0.0aN`), so existing installs are unaffected. **If your package depends on `mcp`, add an upper bound (`mcp>=1.x,<2`) before the stable release lands.**
+> **v1.x is the only stable release line and remains recommended for production.** It is in maintenance mode and continues to receive critical bug fixes and security patches. Installers never select a pre-release unless you opt in (for example `pip install mcp==2.0.0aN`), so existing installs are unaffected. **If your package depends on `mcp`, add a `<2` upper bound to your version constraint (for example `mcp>=1.27,<2`) before the stable release lands.**
 >
 > Try the alpha and tell us what breaks: [#python-sdk-dev on the MCP Contributors Discord](https://discord.gg/6CSzBmMkjX). For v1 documentation, see [the v1.x README](https://github.com/modelcontextprotocol/python-sdk/blob/v1.x/README.md).