Merge pull request #77 from Mic92/imp/contributing-suggestions

[rebased from #67] Suggestions for CONTRIBUTING

CONTRIBUTING.md

@@ -1,6 +1,31 @@
-Profiles should favor usability and stability, so performance hacks should be
-activated by an additional NixOS option or conservative and performance configs
-can be declared in separate profiles.
+# Writing profiles
 
-Because profiles can only be tested with the appropriate hardware, quality
-assurance is up to *you*.
+When setting an option, use `lib.mkDefault` unless:
+- The option *must* be set and the user should get an error if they try to override it.
+- The setting should merge with the user's settings (typical for list or set options).
+
+For example:
+
+```nix
+{ lib }: {
+  # Using mkDefault, because the user might want to disable tlp
+  services.tlp.enable = lib.mkDefault true;
+  # No need to use mkDefault, because the setting will merge with the user's setting
+  boot.kernelModules = [ "tmp_smapi" ];
+}
+```
+
+Try to avoid "opinionated" settings relating to optional features like sound, bluetooth, choice of bootloader etc.
+
+Where possible, use module imports to share code between similar hardware variants.
+
+# Performance
+
+Profiles should favor usability and stability, so performance improvements should either be conservative or 
+be guarded behind additional NixOS module options.
+
+If it makes sense to have a performance-focussed config, it can be declared in a separate profile.
+
+# Testing
+
+Because profiles can only be tested with the appropriate hardware, quality assurance is up to *you*.