Use node16 and asdf

Introduce .tool-versions with newest nodejs 16 and update documentation to reference this file. This way the current node version is saved in one place that can be read by runtime version managing software, eg. https://asdf-vm.com/

Also small restructuring of the installation instruction list, including https://github.com/pietervdvn/MapComplete/pull/483.

.tool-versions

@@ -1 +1 @@
-nodejs 14.14.0
+nodejs 16.9.1

Docs/Development_deployment.md

@@ -26,14 +26,17 @@ Devcontainer (see more details later).
 
 To develop and build MapComplete, you
 
-0. Make sure you have a recent version of nodejs - at least 12.0, preferably 15
 0. Make a fork and clone the repository.
-1. Install `npm`. Linux: `sudo apt install npm` (or your favourite package manager), Windows: install
+0. Install the nodejs version specified in [.tool-versions](./.tool-versions)
+   - You can [use asdf to manage your runtime versions](https://asdf-vm.com/).
+0. Install `npm`. Linux: `sudo apt install npm` (or your favourite package manager), Windows: install
    nodeJS: https://nodejs.org/en/download/
-3. Run `npm run init` and generate some additional dependencies and generated files. Note that it'll install the
+0. Install `wget`, `brew install wget`
-   dependencies too
+0. Run `npm run init` which …
-4. Run `npm run start` to host a local testversion at http://localhost:1234/index.html
+   - runs `npm install`
-5. By default, a landing page with available themes is served. In order to load a single theme, use `layout=themename`
+   - generates some additional dependencies and files
+0. Run `npm run start` to host a local testversion at http://localhost:1234/index.html
+0. By default, a landing page with available themes is served. In order to load a single theme, use `layout=themename`
    or `userlayout=true#<layout configuration>` as [Query parameter](URL_Parameters.md). Note that the shorter URLs (
    e.g. `bookcases.html`, `aed.html`, ...) _don't_ exist on the development version.
 
@@ -125,4 +128,3 @@ Overview of package.json-scripts
 - `deploy:staging`,`deploy:pietervdvn`, `deploy:production`: deploy the latest code on various locations
 - `lint`: get depressed by the amount of warnings
 - `clean`: remove some generated files which are annoying in the repo
-