Move uncritical files into etc/ (#350)

This is mainly just to reduce the amount of files in the project root.
The criteria of what gets into `etc/` are the following:

* The file should not be necessary for building nsxiv. This excludes the
  `icon/*` stuff since that's needed by `window.c`.
* The file shouldn't have any valid reason to stay in the project root.
  This excludes things like `README.md`, `.gitignore` etc.

Reviewed-on: https://codeberg.org/nsxiv/nsxiv/pulls/350
Reviewed-by: explosion-mental <explosion-mental@noreply.codeberg.org>

.github/workflows/build.yml

@@ -21,7 +21,7 @@ jobs:
         ( cd "tinycc-$TCC_SHA" && ./configure && make && sudo make install; )
     - name: build
       run: |
-        CFLAGS="$(sed '/^#/d' .woodpecker/CFLAGS | paste -d ' ' -s)"
+        CFLAGS="$(sed '/^#/d' etc/woodpecker/CFLAGS | paste -d ' ' -s)"
         build () {
           for cc in "gcc" "clang" "tcc"; do
             echo "### $cc - $2 build ###"