Update the instructions for updating licenses. (#51297)

* Adds markdown formatting to better highlight the important bits.
* Removes the bit about patch files not being valid because they are
copied from the GitHub UI (we use LUCI now).
* Add a shortcut for Mac to apply the patch from your pasteboard.

Author: chinmaygarde

tools/licenses/README.md

@@ -1,20 +1,42 @@
 # Update License Files
 
 ## Apply patch generated by CI
-If you're not working on a Linux box then you can't auto-generate license files. A workaround is provided via CI.
-
-Your build will fail one or more CI checks if your license files are not correct. Open the failing CI check. In the CI output you will find a patch diff that represents the changes that need to be made to your license files.
+If you're not working on a Linux box then you can't auto-generate license
+files. A workaround is provided via CI.
+
+Your build will fail one or more CI checks if your license files are not
+correct. Open the failing CI check. In the CI output you will find a
+patch diff that represents the changes that need to be made to your
+license files.
+
+> [!WARNING]
+> Do this only if the diff does not change _which_ licenses are being
+> included, but affects just the `FILE:` metadata and so forth in the
+> golden files. If the actual content of the licenses has changed, you
+> will need to rerun the script from a Linux box to update the actual
+> LICENSE file, as described below.
+
+```sh
+cd flutter/ci/licenses_golden
+```
 
-IF (and only if!) the diff does not change _which_ licenses are being included, but only affects the `FILE:` metadata and so forth in the golden files, then you can click `Download full logs` (Github removes lines with only whitespaces, which invalidates the diff), copy this patch to a temporary patch file wherever you'd like, and then apply the patch to your repo:
+If the file is to `my/patch/file` locally. The `-p2` strips two path
+components from the file paths in the diff. Adjust as necessary.
 
-```
-cd flutter/ci/licenses_golden
+```sh
 patch -p2 < my/patch/file
 ```
 
-HOWEVER, if the actual content of the licenses changed then you will need to rerun the script from a Linux box to update the actual LICENSE file, as described below.
+If the patch file is copied in your clipboard. On Mac, you may apply the patch from there.
+
+```sh
+pbpaste | patch -p2
+```
+
+## Check for license changes
 
-## Check for license changes (Only works on Linux)
+> [!WARNING]
+> Only works on Linux.
 
 This script has two sets of output files: "goldens", which describe
 the current license state of the repository, and the actual real
@@ -46,11 +68,12 @@ cp ../../../out/licenses/* ../../ci/licenses_golden
 git diff
 ```
 
-If the only changes are to what files are included, then you're good
-to go. However, if any of the _licenses_ changed, whether new licenses
-are added, old ones removed, or any have their content changed in
-_any_ way (including, e.g., whitespace changes), or if the affected
-libraries change, **you must update the actual license file**.
+> [!IMPORTANT]
+> If the only changes are to what files are included, then you're good
+> to go. However, if any of the _licenses_ changed, whether new licenses
+> are added, old ones removed, or any have their content changed in
+> _any_ way (including, e.g., whitespace changes), or if the affected
+> libraries change, **you must update the actual license file**.
 
 The `sky/packages/sky_engine/LICENSE` file is the one actually
 included in product releases and the one that should be updated any