priv/static: Add a warning discouraging admins from modifying the static files directly

diff --git a/priv/static/READ_THIS_BEFORE_TOUCHING_FILES_HERE b/priv/static/READ_THIS_BEFORE_TOUCHING_FILES_HERE
new file mode 100644 (file)
index 0000000..eb5294e
--- /dev/null
+++ b/priv/static/READ_THIS_BEFORE_TOUCHING_FILES_HERE
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+If you are an instance admin and you want to modify the instace static files, this is probably not the right place to do it. This directory is checked in version control, so don't be surprised if you get merge conflicts after modifying anything here. Please use instance static directory instead, it has the same directory structure and files placed there will override files placed here. See https://docs.pleroma.social/backend/configuration/static_dir/ for more info