Update README

Author: domesticmouse

tooling/codelab_rebuild/README.md

@@ -30,33 +30,33 @@ At the top level, the `codelab_rebuild.yaml` configuration file contains
 two keys, `name` for the name of the script, and `steps` which is the collection
 of steps required to rebuild the codelab.
 
-Individual steps can have a variety of attributes, which control what the step 
-does. All steps must have a `name` which is output during the run. This is 
+Individual steps can have a variety of attributes, which control what the step
+does. All steps must have a `name` which is output during the run. This is
 primarily for debugging a script when things break.
 
-Steps may have a `steps` for a list of sub steps, in which case it can't have 
+Steps may have a `steps` for a list of sub steps, in which case it can't have
 any other attributes. Steps within steps can go as deep as required.
 
-For removing a file there is `rm`, removing a directory `rmdir`, creating a 
+For removing a file there is `rm`, removing a directory `rmdir`, creating a
 directory there is `mkdir`, each of which takes as the value the path to the
 file or directory to create or remove.
 
-For modifying the content of files there are two approaches. For replacing the 
-contents of a file, there is `replace-contents` key which takes the new contents of 
+For modifying the content of files there are two approaches. For replacing the
+contents of a file, there is `replace-contents` key which takes the new contents of
 the file as the value. Note, if the file doesn't exist, `replace-contents` will \
-create the file. To specify the file to be modified you must also set the 
+create the file. To specify the file to be modified you must also set the
 `path` key with the relative path to the file.
 
-Alternatively there is the `patch` family of keys, which are fed to the `patch` 
-command to update the file nominated by the `path` key. After much trial and 
+Alternatively there is the `patch` family of keys, which are fed to the `patch`
+command to update the file nominated by the `path` key. After much trial and
 error I have stabilised on using `patch-u` (unified diffs), generated with the
 help of the `git diff` command.
 
 For running `flutter` and `dart` commands there are appropriate keys. Use the
 `path` key to nominate the working directory in which to run the `flutter` or
 `dart` command.
 
-There is a `platforms` key to restrict which platforms a step will be run on. 
+There is a `platforms` key to restrict which platforms a step will be run on.
 This is useful for specifying that specific `flutter` commands are only run
-on platforms that support that form of executable. No point trying to build 
-an iOS Flutter app on MS Windows.
+on platforms that support that form of executable. No point trying to build
+an iOS Flutter app on MS Windows.