Add a better ignore script (GoogleChrome#5524)

* Migrate ignore feature from d.c.c.

* Fix an issue with ignored codelabs.

* Add better ignore script and readme update

* gitignore eleventyignore

Author: robdodson

.eleventyignore

@@ -85,3 +85,7 @@ entrypoint.hashmanifest.json
 .tmp
 .firebase
 firebase.json
+
+# Eleventy
+# We generate our own .eleventyignore file dynamically during builds
+.eleventyignore

.gitignore

@@ -2,7 +2,6 @@
   "//1": "Use git commit --no-verify to bypass the pre-commit hook",
   "//2": "Use git push --no-verify to bypass the pre-push hook",
   "hooks": {
-    "pre-push": "npm run lint",
-    "pre-commit": "node ./tools/isolate restored"
+    "pre-push": "npm run lint"
   }
 }

.huskyrc

@@ -48,43 +48,24 @@ npm run dev
 Open `http://localhost:8080/` to see the site locally. Changes to assets will
 rebuild the site. Refresh to see your changes.
 
-### Speeding up builds
+### Set up build flags
 
-⚠️ This is an experimental feature 🧪🔬
+Building the entire site can take a while because it's around one thousand pages.
+If you want to _massively_ speed up your build times, we suggest setting some
+build flags to ignore certain sections.
 
-Any change to the site will cause Eleventy to rebuild. This can take 10-20s. If
-you want to speed things up you can isolate your directory using the `isolate`
-command.
+- Create a `.env` file at the root of your project
+- Add the following:
 
-```bash
-npm run isolate
-```
-
-This will move all of the markdown files for the site into the `_exile`
-directory and it will ignore them for builds.
-
-You may pass an optional glob (or space separated list of globs) to the
-`isolate` command to tell it to preserve a directory.
-
-```bash
-# Example 1: Preserve the style-focus directory
-# note the -- which is needed to pass options to npm scripts
-npm run isolate -- src/site/content/en/accessible/style-focus/**
+```text
+# Ignore ALL site content
+ELEVENTY_IGNORE=true
 
-# Example 2: Preserve everything in the accessible directory
-npm run isolate -- src/site/content/en/accessible/**/*
+# Only build the directories you're working on.
+# Note, this is a JSON string so you must use double quotes.
+ELEVENTY_INCLUDE=["blog", "vitals"]
 ```
 
-When you're finished making your edits, run the `integrate` command to restore
-all of the project files.
-
-```bash
-npm run integrate
-```
-
-☝️ A git commit hook will prevent you from being able to run `git commit` until
-you have run the `integrate` command.
-
 ## Environments 🌳
 
 Set `ELEVENTY_ENV=prod` to force production builds. This is the default when
@@ -116,7 +97,7 @@ teams:
 - @GoogleChrome/web-devrel
 
 1. Navigate to [the Deploy workflow in the Actions panel](https://github.com/GoogleChrome/web.dev/actions?query=workflow%3ADeploy).
-2. Click the **Run workflow** button. Make sure the branch says `master`, then click the green **Run workflow** button.
+2. Click the **Run workflow** button. Make sure the branch says `main`, then click the green **Run workflow** button.
 
 ![An expanded workflow popup with a green run workflow button inside of it.](https://user-images.githubusercontent.com/1066253/89584965-da6eb500-d7f1-11ea-8a43-d8b1abe2cd3b.png)