Adding troubleshooting information about Subresource Integrity digests. (facebook#1220)

Author: dfbaskin

packages/react-scripts/template/README.md

@@ -61,6 +61,7 @@ You can find the most recent version of this guide [here](https://github.com/fac
 - [Troubleshooting](#troubleshooting)
   - [`npm test` hangs on macOS Sierra](#npm-test-hangs-on-macos-sierra)
   - [`npm run build` silently fails](#npm-run-build-silently-fails)
+  - [Subresource integrity checks fail](#subresource-integrity-checks-fail)
 - [Something Missing?](#something-missing)
 
 ## Updating to New Releases
@@ -1244,6 +1245,17 @@ There are also reports that *uninstalling* Watchman fixes the issue. So if nothi
 
 It is reported that `npm run build` can fail on machines with no swap space, which is common in cloud environments. If [the symptoms are matching](https://github.com/facebookincubator/create-react-app/issues/1133#issuecomment-264612171), consider adding some swap space to the machine you’re building on, or build the project locally.
 
+### Subresource integrity checks fail
+
+[Subresource Integrity](https://developer.mozilla.org/en-US/docs/Web/Security/Subresource_Integrity) digests are added to the build output files. For a particular scenario, these checks may fail when deployed. The files are built using `LF` characters, but if your deployment uses a Git repository for deployment (like Azure web sites) and the Git repository is set up to translate `LF` characters into `CR/LF` characters, then the checked out files will be different and the digests will be invalid.
+
+To fix this, just add a `.gitattributes` file to your deployment repository that will ensure the build files are not modified when checked out:
+
+```
+*.css text eol=lf
+*.js text eol=lf
+```
+
 ## Something Missing?
 
 If you have ideas for more “How To” recipes that should be on this page, [let us know](https://github.com/facebookincubator/create-react-app/issues) or [contribute some!](https://github.com/facebookincubator/create-react-app/edit/master/packages/react-scripts/template/README.md)