Docs: update installation command to use specific version tag

[tuhaihe]

Update the installation instructions in README.md to use the specific version tag @2.1.0-incubating instead of @latest.

The @latest tag resolves to v1.0.2 due to Go modules semantic versioning rules, which only recognizes version tags with 'v' prefix (v1.0.0, v1.0.1, v1.0.2). The 2.1.0-incubating tag, while functional when specified directly, is not recognized as a semantic version by Go modules.

Added a note to clarify why users should use the specific version tag to avoid confusion and ensure they install the correct latest version.

closes: #ISSUE_Number

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[woblerr]

LGTM, thanks