Add notes concerning privacy and network access

Author: lnicola

PRIVACY.md

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+# Privacy Notes
+
+## LSP server binary
+
+The LSP server performs no network access in itself, but runs `cargo metadata` which will update or download the crate registry and the source code of the project dependencies.
+
+## Visual Studio Code extension
+
+The Code extension connects to GitHub to download updated LSP binaries and, if the nightly channel is selected, to perform update checks.
+
+## Other editor plugins
+
+Any other editor plugins that integrate with `rust-analyzer` are not under the control of the `rust-analyzer` developers. For any privacy concerns, you should check with their respective developers.
+
+## Others
+
+If `cargo check` is enabled (the default), any build scripts or procedural macros used by the project or its dependencies will be executed. This is also the case when `cargo check` is disabled, but build script or procedural macro support is enabled in `rust-analyzer` (off by default).