Add reasonable instructions for uprgrading a Portable edition

Author: pryrt

content/docs/upgrading.md

@@ -15,9 +15,6 @@ Using the **? > Update Notepad++** menu command. This will check whether there i
 ## Upgrade Manually
 Going to the main website and downloading the latest installer and running it yourself.  You can watch the [Announcements](https://community.notepad-plus-plus.org/category/1/announcements) category in the [Notepad++ Community Forum](https://community.notepad-plus-plus.org/) to see when new release-candidates or final versions are released.
 
-## Download Zip Package
-Going to the main website and downloading the latest zipped archive.  You can then use it as a separate portable version, or compare its files to another installed or portable version, so you can decide how and when to upgrade.
-
 ## No New Version Found: Safety Delay
 There are two reasons that would cause there to be no new version found during an auto-triggered upgrade check or an on-demand upgrade check:
 
@@ -29,3 +26,41 @@ The safety delay will never prevent you from downloading the installer or portab
 
 ## WinGUp Project
 The [WinGUp](http://wingup.org/) project was started for the need of Notepad++ for upgrading Notepad++ automatically.  It has since become a more generic solution for updating purposes. [This project has been forked](https://github.com/notepad-plus-plus/wingup) for more Notepad++ specific need so Plugin Admin can share its basic functionalities.
+
+## Download Zip Package
+Going to the main website and downloading the latest zipped archive.  You can then use it as a separate portable version (which isn't technically upgrading, but will allow to try out a new version before upgrading), or compare its files to another installed or portable version, so you can decide how and when to upgrade.
+
+### Upgrading a Portable Edition
+
+If you have a portable edition of Notepad++, unzipping the contents from the new zipfile into your old directory will overwrite some of your configuration files, including `config.xml`, which will mean you will lose your customized settings.  A recommended workflow for upgrading a portable edition (with dummy directories; you can choose whatever directories are convenient):
+
+1. Starting condition:
+    - Your original installation is in `c:\PortableNpp\`
+    - You have the ComparePlus plugin, or otherwise understand how to compare contents of similar files
+    - You have read and understood the [Online UserManual section on Editing Configuration Files](https://npp-user-manual.org/docs/config-files/#editing-configuration-files)
+    - Make sure you have recently exited Notepad++ and restarted it, without having made any configuration changes in the GUI since restarting it, as per "Editing Configuration Files".
+2. Unzip the new portable zipfile into `c:\PortableNpp.new\`
+3. Compare each of the following configuration files.  Look for any settings that are in the New but not in the Old, and copy them over.
+    - **Optional**: For some, the updates in the configuration files usually just give access to new features which you might not care about (like a new right-click menu action); in that case, it is up to you to decide whether you want to bring over the new features or not.
+    - **Overwrite**: For these configuration files, users rarely customize them.  Unless you know that you have, it's generally safe to just overwrite it with the new copy.
+    - **Model**: For these configuration files, you will be comparing your raw file with the new `.model.` version.  These are files that are often customized, so when you are comparing, you will want to be careful to bring over the new features (things that are in the new `.model.`) without getting rid of your customizations.
+
+    | Old (`c:\PortableNpp\...`) | New (`c:\PortableNpp.new\...`) | Notes |
+    |-----|-----|-------|
+    | `...\config.xml` | `...\config.xml` | |
+    | `...\contextMenu.xml` | `...\contextMenu.xml` | Optional |
+    | `...\shortcuts.xml` | `...\shortcuts.xml` | Optional |
+    | `...\toolbarIcons.xml` | `...\toolbarIcons.xml` | Optional |
+    | `...\langs.xml` | `...\langs.model.xml` | Model |
+    | `...\stylers.xml` | `...\stylers.model.xml` | Model |
+    | `...\themes\___.xml` | `...\themes\____.xml` | Overwrite ¹ |
+    | `...\autoCompletion\___.xml` | `...\autoCompletion\____.xml` | Overwrite |
+    | `...\localization\___.xml` | `...\localization\____.xml` | Overwrite |
+    | `...\functionList\___.xml` | `...\functionList\____.xml` | Overwrite |
+    | `...\userDefineLangs\___.xml` | `...\userDefineLangs\____.xml` | Overwrite |
+
+    - ¹: If you are using a specific theme, it's more likely that you will have customized that theme's file.  Please do a full comparison on that theme file, but you can probably get away with just overwriting the old theme files.
+
+4. After updating the config files, then you can exit Notepad++, copy the `notepad++.exe` and `plugins\config\nppPluginList.dll` from the old to the new, and restart Notepad++ to start using your upgraded portable edition.
+
+_Note: a similar procedure can be used when you think your installed copy of Notepad++ has themes or syntax highlighting configuration that is missing compared to a fresh install or portable, except you would use `%AppData%\Notepad++\____.xml` and/or `C:\Program Files\Notepad++\____.xml` as the **Old** location, instead of a portable location._