Clarify behavior of of overrides in CLI reference (#7537)

## Summary
Improve the description of override-dependencies based on the statement
in `concepts/resolution.md`: "As with constraints, overrides do not add
a dependency on the package and only take effect if the package is
requested in a direct or transitive dependency."

I tested it locally, `concepts/resolution.md` is correct. It would be
better to also include this in the Reference Chapter of the docs.

crates/uv-workspace/src/pyproject.rs

@@ -230,6 +230,10 @@ pub struct ToolUv {
     /// constituent packages, overrides are _absolute_, in that they completely replace the
     /// requirements of any constituent packages.
     ///
+    /// Including a package as an override will _not_ trigger installation of the package on its
+    /// own; instead, the package must be requested elsewhere in the project's first-party or
+    /// transitive dependencies.
+    ///
     /// !!! note
     ///     In `uv lock`, `uv sync`, and `uv run`, uv will only read `override-dependencies` from
     ///     the `pyproject.toml` at the workspace root, and will ignore any declarations in other

docs/reference/settings.md

@@ -103,6 +103,10 @@ While constraints are _additive_, in that they're combined with the requirements
 constituent packages, overrides are _absolute_, in that they completely replace the
 requirements of any constituent packages.
 
+Including a package as an override will _not_ trigger installation of the package on its
+own; instead, the package must be requested elsewhere in the project's first-party or
+transitive dependencies.
+
 !!! note
     In `uv lock`, `uv sync`, and `uv run`, uv will only read `override-dependencies` from
     the `pyproject.toml` at the workspace root, and will ignore any declarations in other