README.md : Added "Creating a Gentoo's patch" notes

README.md

@@ -225,3 +225,27 @@ e2fsck -f $FS
 resize2fs $FS $SIZE
 mount $FS $MOUNT_POINT
 ```
+
+## Creating a Gentoo's patch
+
+### Using diff
+
+```sh
+tar -xvf /var/cache/distfiles/package.tar.xz
+mv package a
+cp -r a b
+# Make your changes to b.
+diff -ur a b > /etc/portage/patches/example-category/example-packagename/my-patch.patch
+```
+
+### Using git
+
+```sh
+tar -xvf /var/cache/distfiles/package.tar.xz
+cd package
+git init
+git add .
+git commit -m "Initial commit"
+# Make your changes
+git diff > /etc/portage/patches/example-category/example-packagename/my-patch.patch
+```