Document Offline mode with feature flags
I ran into this and found the solution inside of this issue
Fixes
@@ -126,3 +126,13 @@ variable to `true`.
If you want to make this the default, just add it to your `.env` file. `cargo sqlx prepare` will
still do the right thing and connect to the database.
+
+#### Include queries behind feature flags (such as queryies inside of tests)
+
+In order for sqlx to be able to find queries behind certain feature flags you need to turn them
+on by passing arguments to rustc.
+
+This is how you would turn all targets and features on.
+```bash
+cargo sqlx prepare -- --all-targets --all-features
+```
