Update manifest.md

Remove comment from example toml to prose.

Author: jorendorff

src/doc/src/reference/manifest.md

@@ -361,10 +361,12 @@ script guide.
 
 [links]: build-scripts.md#the-links-manifest-key
 
+For example, a crate that links a native library called "git2" (e.g. `libgit2.a`
+on Linux) may specify:
+
 ```toml
 [package]
 # ...
-# this package links with a native library called "git2", e.g. "libgit2.a" on Linux
 links = "git2"
 ```