Add a DEBUGGING.md file with some information useful for debugging

I have included information about various things I've used for debugging
COSMIC. More could definitely be added.

It seems good to have some central resource for this. Though not
everything listed here is very straightforward to use.

scripts/tag.sh

@@ -1,29 +0,0 @@
-#!/usr/bin/env bash
-
-set -e
-
-TAG="$1"
-
-if [ -z "$TAG" ]
-then
-    echo "$0 [tag]" >&2
-    exit 1
-fi
-
-echo "Do you want to tag the current state of cosmic-epoch with the tag $TAG? (y/N)"
-read answer
-if [ "$answer" != "y" ]
-then
-    echo "Did not answer y, exiting" >&2
-    exit 1
-fi
-
-set -x
-
-git fetch --recurse-submodules
-
-git tag --force "$TAG"
-git submodule foreach git tag --force "$TAG"
-
-git push --force origin tag "$TAG"
-git submodule foreach git push --force origin tag "$TAG"