Auto merge of #3065 - mbrock:master, r=alexcrichton

doc: mention feature toggling in "Specifying deps"

Basically copies info that was already on another page.

src/doc/specifying-dependencies.md

@@ -391,3 +391,19 @@ unless listed under the `dependencies` section as well. A package
 itself and its build script are built separately, so their
 dependencies need not coincide. Cargo is kept simpler and cleaner by
 using independent dependencies for independent purposes.
+
+# Choosing features
+
+If a package you depend on offers conditional features, you can
+specify which to use:
+
+```toml
+[dependencies.awesome]
+version = "1.3.5"
+default-features = false # do not include the default features, and optionally
+                         # cherry-pick individual features
+features = ["secure-password", "civet"]
+```
+
+More information about features can be found in the
+[manifest documentation](manifest.html#the-features-section).