prepare to add release texts

res/releaseReadme/stable-linux.txt

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+# Furnace (chiptune tracker)
+
+thank you for downloading Furnace! I hope you enjoy using it.
+
+extract this archive, and run `furnace` to get started.

res/releaseReadme/stable-mac.txt

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+# Furnace (chiptune tracker)
+
+thank you for downloading Furnace! I hope you enjoy using it.
+
+move Furnace to Applications (or some other place).
+if you are using a recent version of macOS, you may get an error saying that Furnace is damaged.
+in that case, open Terminal, and type this:
+
+```
+xattr -d com.apple.quarantine /path/to/Furnace.app
+```
+
+(replace `/path/to/Furnace.app` with the path where Furnace.app is located, e.g. `/Applications/Furnace.app`)
+
+you may need to reboot after doing this before launching Furnace.

res/releaseReadme/stable-win.txt

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+# Furnace (chiptune tracker)
+
+thank you for downloading Furnace! I hope you enjoy using it.
+
+extract this archive, and run furnace.exe to get started.

res/releaseReadme/unstable-other.txt

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+# unstable build notice
+
+this is a dev build (also known as "unstable", "artifact" or "nightly").
+it may contain work-in-progress features and/or bug fixes.
+
+no compatibility is guaranteed between unstable and stable - you have been warned!

res/releaseReadme/unstable-win.txt

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+# unstable build notice
+
+this is a dev build (also known as "unstable", "artifact" or "nightly").
+it may contain work-in-progress features and/or bug fixes.
+
+no compatibility is guaranteed between unstable and stable - you have been warned!
+
+# the .pdb file
+
+YOU SHALL COPY THIS FILE ALONGSIDE furnace.exe. it contains debug information which is vital in the moment of a crash.
+failure to copy this file will result in useless backtraces (furnace_crash.txt) and therefore hinder me from fixing any crashes.