docs: Document that you need Scala 3.4 or 2.13.x with -Xsource:3

Closes #88

site-in/other-features/flexible.md

@@ -9,7 +9,9 @@ of integrating Typo piece-by-piece into your code base.
 
 ## Developed in the Scala 2/3 shared subset
 
-Everything works on Scala 2.13 and 3.3.
+Everything works on Scala 2.13 and 3.4. 
+
+For *2.13* you need to set add `-Xsource:3` to `scalacOptions`. The shared subsets shrinks in size for every Scala 3 release, unfortunately.
 
 ## Bring your own DB library
 

site-in/setup.md

@@ -35,7 +35,7 @@ put it in `gen-db.sc` and run `scala-cli gen-db.sc`
 // remember to give the project a github star if you like it <3
 //
 //> using dep "com.olvind.typo::typo:@VERSION@"
-//> using scala "3.3.0"
+//> using scala "3.4.0"
 
 import typo.*
 
@@ -72,6 +72,11 @@ generateFromDb(options, targetFolder = targetDir, selector = selector, scriptsPa
 //scala.sys.process.Process(List("git", "add", targetDir.toString)).!!
 ```
 
+## Compiling the generated code
+
+For **Scala 2** you need to set add `-Xsource:3` to `scalacOptions`, with a recent version of Scala 2.13.
+For **Scala 3** you'll need 3.4.0 or later.
+
 ## `selector`
 You can customize which relations you generate code for, see [customize selected relations](customization/customize-selected-relations.md)