docs: add Installation page (uv install path)

docs/INSTALLATION.md

@@ -0,0 +1,61 @@
+## Requirements
+
+This guide uses uv, a fast Python package and project manager, to install and manage MkDocs and its dependencies. MkDocs 2.0's pre-release currently requires Python 3.10 or later — uv can fetch a suitable Python version for you automatically, so you don't need one already on your system.
+
+You can check if you already have uv installed from the command line:
+
+```shell
+uv --version
+```
+
+If uv is installed, this prints a version number (something like `uv 0.12.13 ...`). If instead you see something like `command not found: uv`, follow the steps below to install it.
+
+### Installing uv
+
+Install uv using the standalone installer:
+
+```shell
+curl -LsSf https://astral.sh/uv/install.sh | sh
+```
+
+If `uv` isn't recognized as a command right after installing, load it into your current shell session:
+
+```shell
+source $HOME/.local/bin/env
+```
+
+## Installing MkDocs
+
+Install the mkdocs package using uv, allowing pre-release versions:
+
+```shell
+uv tool install mkdocs --prerelease allow
+```
+
+Note: this is *not* the same as pip's `--pre` flag — uv doesn't recognize `--pre` as a prerelease toggle at all, and will silently install the latest stable release instead, with no warning.
+
+Verify what actually got installed:
+
+```shell
+uv tool list
+```
+
+This should show `mkdocs` at a `2.0.dev` version. If it shows an older `1.x` version instead, it's because uv didn't have a Python 3.10+ interpreter available to use for it. Check what uv has:
+
+```shell
+uv python list
+```
+
+If nothing 3.10 or newer shows as already installed (rather than just "download available"), fetch one (any version 3.10 or later — 3.12 is used here as the example):
+
+```shell
+uv python install 3.12
+```
+
+Then install again, specifying that interpreter directly:
+
+```shell
+uv tool install mkdocs --prerelease allow --python 3.12
+```
+
+Run `uv tool list` again to confirm.