Ports: Explain some new patch script options and features in the README

This explains:
- `package.sh dev [--no-depends]`
- `use_fresh_config_sub` & `config_sub_path`

Ports/README.md

@@ -88,6 +88,24 @@ By default, [`clean`](#clean) and [`clean_dist`](#clean_dist) combined.
 Remove the port's files from the Serenity build directory, if it has a `plist`
 file.
 
+#### `dev`
+
+Start a development session with guided patch importing.
+This mode has a bunch of nice features:
+
+- Drops the user in a git repository backed by another (local) git repository
+  that acts as the "clean", patched version of the port that is ready to be built
+- The "remote" repository can be pushed to, pulled from and generally anything that
+  you'd want to do with a remote repo.
+- After leaving the dev shell, all patches are updated and the user will be prompted
+  whether they wish to generate a new patch readme file.
+
+This mode takes an extra `--no-depends` option, that if given, will cause the dependency
+fetch and build steps to be skipped.
+
+This mode can also assist in migrating old patches to new versions through a guided
+semi-automated process.
+
 #### `--auto`
 
 Same as no option, but mark the port as having been installed automatically.
@@ -151,6 +169,16 @@ Options passed to the port's [`configscript`](#configscript) in the default
 `--host=i686-pc-serenity` is always passed, override the `configure` function
 if that's undesirable.
 
+#### `use_fresh_config_sub`
+
+Boolean option (`false` by default), will replace the `config.sub` pointed to by
+`config_sub_path` as part of the patching process if set to true.
+
+#### `config_sub_path`
+
+Path to the `config.sub` file used by autoconf, starting at `$workdir`.
+This is set to `config.sub` by default.
+
 #### `configscript`
 
 Name of the script that will be run in the default `configure` function when