Considerable cleanup of installation docs

docs/source/Setup/Installation-Upgrade.md

@@ -0,0 +1,44 @@
+# Upgrading an existing installation
+
+These are steps to take when you have an _exiting game dir that you want to keep_. 
+If you don't, you can always just delete your old game dir and initialize a fresh one using 
+the normal [install instructions](./Installation.md).
+
+## Evennia v0.9.5 to  1.0
+
+Prior to 1.0, all Evennia installs were [Git-installs](./Installation-Git.md). These instructions
+assume that you have a cloned `evennia` repo and use a virtualenv (best practices).
+
+- Make sure to stop Evennia 0.9.5 entirely with `evennia stop`.
+- `deactivate` to leave your active virtualenv.
+- Make a _backup_ of your entire `mygame` folder, just to be sure! 
+- Delete the old `evenv` folder, or rename it (in case you want to keep using 0.9.5 for a while).
+
+
+- Install Python 3.10 (recommended) or 3.9. Follow the [Git-installation](./Installation-Git.md) for your OS if needed.
+- If using virtualenv, make a _new_ one with `python3.10 -m venv evenv`, then activate with `source evenv/bin/activate`
+  (linux/mac) or `\evenv\Script\activate` (windows)
+- `cd` into your `evennia/` folder (you want to see the `docs/`, `bin/` directories as well as a nested `evennia/` folder)
+- **Prior to 1.0 release only** - do `git checkout develop` to switch to the develop branch. After release, this will
+  be found on the default master branch.
+- `git pull` 
+- `pip install -e .`
+- If you want the optional extra libs, do `pip install -r requirements_extra.txt`.
+- Test that you can run the `evennia` command.
+
+
+- Next, `cd` to your game folder (like `mygame`.)
+- If you have changed `mygame/web`, _rename_ the folder to `web_0.9.5`. If you didn't change anything (or don't have 
+anything you want to keep), you can _delete_ it entirely.
+- Copy `evennia/evennia/game_template/web` to `mygame/` (e.g. using `cp -Rf` or a file manager). This new `web` folder
+replaces the old one and has a very different structure.
+- `evennia migrate`
+- `evennia start`
+
+If you made extensive work in your game dir, you may well find that you need to do some (hopefully minor) 
+changes to your code before it will start with Evennia 1.0. Some important points: 
+
+- The `evennia/contrib/` folder changed structure - there are now categorized sub-folders, so you have to update 
+your imports.
+- Any `web` changes need to be moved back from your backup into the new structure of `web/` manually.
+- See the [Evennia 1.0 Changelog](./Changelog.md) for all changes.