Merge pull request #1132 from amitaibu/patch-6

Doc for Type errors in `build/Generated/Types.hs`

CONTRIBUTING.md

@@ -149,6 +149,19 @@ Perhaps a package was added to IHP recently. Start a `nix-shell` in the IHP dire
 
 Either add the package to your project's `default.nix` as well, or change the section `ihp = builtins.fetchGit ...` to `ihp = ./IHP;`in your project's `default.nix`. Then the `IHP/ihp.nix` will be used to fetch packages.
 
+### Type errors in `build/Generated/Types.hs`
+
+The errors comes from changes to the Schema Compiler, so `build/Generated/Types.hs` is outdated. The error only happens when we have backwards compatibility breaks in some of the interfaces, which doesn't happen very often. If you do get them you should execute from `IHP` directory
+
+```
+nix-shell
+ghci
+:l IHP/IHP/SchemaCompiler.hs
+compile
+```
+
+After this the error should be gone, and you can go back to `:l Main`
+
 ### Reverting back to running with stock IHP library
 
 If you want to go back and use the standard IHP library instead of the cloned source, for instance when your much needed, contributed and approved feature becomes part of the release, then in your project directory: