Explain about Manifest.toml per julia version (#3791)

* Explain about Manifest.toml per julia version

Co-authored-by: Kristoffer Carlsson <kcarlsson89@gmail.com>

docs/src/toml-files.md

@@ -128,6 +128,17 @@ For the details, see [`Pkg.instantiate`](@ref).
     The `Manifest.toml` file is generated and maintained by Pkg and, in general, this file
     should *never* be modified manually.
 
+### Different Manifests for Different Julia versions
+
+Starting from Julia v1.11, there is an option to name manifest files in the format `Manifest-v{major}.{minor}.toml`.
+Julia will then preferentially use the version-specific manifest file if available.
+For example, if both `Manifest-v1.11.toml` and `Manifest.toml` exist, Julia 1.11 will prioritize using `Manifest-v1.11.toml`.
+However, Julia versions 1.10, 1.12, and all others will default to using `Manifest.toml`.
+This feature allows for easier management of different instantiated versions of dependencies for various Julia versions.
+Note that there can only be one `Project.toml` file. While `Manifest-v{major}.{minor}.toml` files are not automatically 
+created by Pkg, users can manually rename a `Manifest.toml` file to match
+the versioned format, and Pkg will subsequently maintain it through its operations.
+
 
 ### `Manifest.toml` entries