Added Update-Instructions.txt

Update-Instructions.txt

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+How to Update SillyTavern
+
+Windows/MacOS: 
+
+Method 1 - GIT
+
+We always recommend users install using 'git'. Here's why: 
+
+When you have installed via `git clone`, all you have to do to update is type `git pull` in a command line in the ST folder. 
+The updates are applied automatically and safely.
+
+Method 2 - ZIP
+
+If you insist on installing via a zip, here is the tedious process for doing the update: 
+
+1. Download the new release zip.
+2. Unzip it into a folder OUTSIDE of your current ST installation.
+3. Do the usual setup procedure with start.bat to install NodeJS requirements. 
+
+4. Copy the following files/folders as necessary(*) from your old ST installation: 
+
+  - Backgrounds
+  - Characters
+  - Chats
+  - Groups
+  - Group chats
+  - KoboldAI Settings
+  - NovelAI Settings
+  - OpenAI Settings
+  - TextGen Settings (textgen = ooba)
+  - Themes
+  - User Avatars
+  - Worlds
+  - settings.json
+
+  (*) 'As necessary' = "If you made any custom content related to those folders". 
+  None of the folders are mandatory, so only copy what you need.
+
+  **NB: DO NOT COPY THE ENTIRE /PUBLIC/ FOLDER.**
+  Doing so could break the new install and prevent new features from being present.
+
+5. Paste those items into the /Public/ folder of the new install. 
+
+6. Run start.bat once again, and pray you got it right. :) 
+
+7. If everything shows up, you can safely delete the old ST folder.
+
+Linux/Termux: 
+
+You definitely installed via git, so just 'git pull' inside the SillyTavern directory.