README.md in heroku_hatchet-4.0.7 vs README.md in heroku_hatchet-4.0.8

@@ -128,10 +128,16 @@
 Hatchet::Runner.new('no_lockfile')
 ```
 
 If you have conflicting names, use full paths.
 
+If you woud like to test with fixtures that are checked in locally, that is also possible by passing in the path to the fixture directory and skipping the `hatchet install`:
+
+```
+Hatchet::Runner.new("spec/fixtures/repos/node-10-metrics")
+```
+
 A word of warning on including repos inside of your test
 directory, if you're using a runner that looks for patterns such as
 `*_test.rb` to run your hatchet tests, it may incorrectly think you want
 to run the tests inside of the repos. To get rid of this
 problem move your repos direcory out of `test/` or be more specific
@@ -252,10 +258,49 @@
     bash.run("cat Procfile") {|result| assert_match "web:", result }
   end
 end
 ```
 
-Please read the docs on [repl_runner](http://github.com/schneems/repl_runner) for more info. The only interactive commands that are supported out of the box are `rails console`, `bash`, and `irb` it is fairly easy to add your own though:
+Please read the docs on [repl_runner](http://github.com/schneems/repl_runner) for more info. The only interactive commands that are supported out of the box are `rails console`, `bash`, and `irb` it is fairly easy to add your own though.
+
+## Modify Application Files on Disk
+
+While template apps provided from your `hatchet.json` can provide a wide array of different test cases, it's likely that you'll want to test minor varriations of an app. To do this you can use the `before_deploy` hook to modify files on disk inside of an app in a way that is threadsafe and will only affect the local instance of the app:
+
+```ruby
+Hatchet::App.new("default_ruby", before_deploy: { FileUtils.touch("foo.txt")}).deploy do
+  # Assert stuff
+end
+```
+
+After the `before_deploy` block fires, the results will be committed to git automatically before the app deploys.
+
+You can also manually call the `before_deploy` method:
+
+```ruby
+app  = Hatchet::App.new("default_ruby")
+app.before_deploy do
+  FileUtils.touch("foo.txt")
+end
+app.deploy do
+  # Assert stuff
+end
+```
+
+Note: If you're going to shell out in this `before_deploy` section, you should check the success of your command, for example:
+
+```ruby
+before_deploy = Proc.new do
+  cmd = "bundle update"
+  output = `#{cmd}`
+  raise "Command #{cmd.inspect} failed unexpectedly with output: #{output}"
+end
+Hatchet::App.new("default_ruby", before_deploy: before_deploy).deploy do
+  # Assert stuff
+end
+```
+
+It's helpful to make a helper function in your library if this pattern happens a lot in your app.
 
 ## Heroku CI
 
 Hatchet supports testing Heroku CI.