Add more information about cargo deny

deny.toml

@@ -52,7 +52,7 @@ name = "ring"
 version = "*"
 expression = "MIT AND ISC AND OpenSSL"
 license-files = [
-    { path = "LICENSE", hash = 0xbd0eed23 },
+    { path = "LICENSE", hash = 0xbd0eed23 }
 ]
 
 [licenses.private]

docs/sourcetree.md

@@ -18,10 +18,6 @@ Intended to be used in integration tests and in CLI tools for local installation
 Documentation of the Neon features and concepts.
 Now it is mostly dev documentation.
 
-`/monitoring`:
-
-TODO
-
 `/pageserver`:
 
 Neon storage service.
@@ -98,6 +94,13 @@ cargo hakari manage-deps
 
 If you don't have hakari installed (`error: no such subcommand: hakari`), install it by running `cargo install cargo-hakari`.
 
+### Checking Rust 3rd-parties
+[Cargo deny](https://embarkstudios.github.io/cargo-deny/index.html) is a cargo plugin that lets us lint project's dependency graph to ensure all dependencies conform to requirements. It detects security issues, matches licenses, and ensures crates only come from trusted sources.
+
+```bash
+cargo deny check
+```
+
 ## Using Python
 Note that Debian/Ubuntu Python packages are stale, as it commonly happens,
 so manual installation of dependencies is not recommended.