Rename 'link-args' to 'advanced-linking', add intro

Author: aidanhs

src/doc/trpl/SUMMARY.md

@@ -63,7 +63,7 @@
     * [No stdlib](no-stdlib.md)
     * [Intrinsics](intrinsics.md)
     * [Lang items](lang-items.md)
-    * [Link args](link-args.md)
+    * [Advanced linking](advanced-linking.md)
     * [Benchmark Tests](benchmark-tests.md)
     * [Box Syntax and Patterns](box-syntax-and-patterns.md)
     * [Slice Patterns](slice-patterns.md)

src/doc/trpl/link-args.md renamed to src/doc/trpl/advanced-linking.md

@@ -1,4 +1,11 @@
-% Link args
+% Advanced Linking
+
+The common cases of linking with Rust have been covered earlier in this book,
+but supporting the range of linking possibilities made available by other
+languages is important for Rust to achieve seamless interaction with native
+libraries.
+
+# Link args
 
 There is one other way to tell rustc how to customize linking, and that is via
 the `link_args` attribute. This attribute is applied to `extern` blocks and