Add ddev setup (really copied from ddev docs but apparently i need the reiteration)

tools/ddev-local-development-environment.md

@@ -0,0 +1,25 @@
+# Local development environments with ddev
+
+We are broadly moving to [ddev](https://ddev.readthedocs.io/en/stable/) from Vagrant.
+
+## Installing ddev
+
+First, install [Homebrew](https://brew.sh/).
+
+Then:
+
+```
+brew tap drud/ddev && brew install ddev
+```
+
+## Updating ddev
+
+```
+ddev poweroff && brew upgrade ddev
+```
+
+Don't forget the poweroff part or it breaks SSH until you run it.
+
+## Using ddev
+
+See [creating new Drutopia sites](tools/creating-new-drutopia-site) for per-site ddev configuration.