rename, update overlays/README.md

overlays/README.md

@@ -1,9 +1,20 @@
-# backports
-This is a nixpkgs overlay that contains temporary fixes for build failures or
-other issues, usually backported from the nixpkgs master branch. Each package
-defined in this overlay shall automatically disable itself once a certain
-condition is met, such as the upstream package being updated or the nixpkgs
-modification date passing a certain time.
+# Overlays
+This directory contains nixpkgs overlays which each serve some specific purpose.
+
+## backports
+This overlay defines programs that should be unconditionally backported from
+nixpkgs-unstable. Packages backported in this overlay will be built using
+inputs from the current system when possible, as to not unnecessarily increase
+the closure size. This may result in unexpected breakages, as packages in
+nixpkgs-unstable are built and tested against other such packages.
+
+
+## mitigations
+This overlay contains temporary fixes for build failures or other issues,
+usually backported from the nixpkgs master branch. Each package defined in this
+overlay shall automatically disable itself once a certain condition is met,
+such as the upstream package being updated or the nixpkgs modification date
+passing a certain time.
 
 This is in place because I am extremely forgetful; I will almost certainly
 forget to undo a temporary fix later, so this takes care of it for me.