Doc: clarify priority of lint level sources

This updates the rustc book to clearly document how conflicting lint configurations are resolved across different sources, including command-line flags, crate-level attributes, in-line attributes, and `--cap-lints`.

It also explains the special behavior of `forbid` and `force_warn`.

Author: HamidrezaSK

src/doc/rustc/src/lints/levels.md

@@ -331,3 +331,22 @@ $
 This feature is used heavily by Cargo; it will pass `--cap-lints allow` when
 compiling your dependencies, so that if they have any warnings, they do not
 pollute the output of your build.
+
+## Priority of Lint Level Sources
+
+Rust allows setting lint levels (`allow`, `warn`, `deny`, etc.) through various sources: directly in the code, via command-line flags, or through global compiler configuration. When these sources conflict, the compiler follows a well-defined priority order to determine which setting takes effect.
+
+This section explains how Rust resolves conflicts between **different sources of lint configuration**, rather than between the lint levels themselves.
+
+### Priority of Sources (Highest to Lowest)
+
+```
+--cap-lints >
+in-line attributes (#[...]) >
+crate-level attributes (#![...]) >
+command-line flags (-A, -W, -D)
+```
+
+### Special Cases
+
+The special levels `forbid(lint)` and `force_warn(lint)` take precedence over normal configurations **regardless of where they are set**.