Direct users to modify dependencies via files rather than CLI commands

The former seems to be falling out of favor, and may confuse users about
which is preferable to use.

Author: afeld

README.md

@@ -55,29 +55,19 @@ files](docs/FAQ.md#what-external-tools-are-supported) to convert
 
 ### Day-to-day workflow
 
-When you or a collaborator add/remove/change dependencies, run
+When you or a collaborator add/remove/change dependencies by modifying
+your `import`s or `Gopkg.toml`, run
 
 ```sh
 $ dep ensure
 ```
 
 This will synchronize your dependencies in `vendor/` to make sure they match
 what's in your `import`s and `Gopkg.toml`. `dep ensure` is safe to run early and
-often.
-
-#### Updating a specific dependency
-
-To update a dependency to a new version, you might run
-
-```sh
-$ dep ensure github.com/pkg/errors@^0.8.0
-```
-
-See the help text for more detailed usage instructions.
+often. See the help text for more detailed usage instructions.
 
 ```sh
 $ dep help ensure
-$ dep ensure -examples
 ```
 
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