translation-instructions.md: Add Solus-MTT info

docs/packaging/translation-instructions.md

@@ -5,8 +5,21 @@ summary: Instructions for translators
 
 # Translation instructions
 
-🚧 This page is a stub for now.
-
 Users will arrive here from the "Translation instructions" link on Transifex.
 
 Please join our [Matrix rooms](/docs/user/contributing/getting-involved.md#matrix-chat) if you have questions about our translation projects.
+
+## Project specific instructions
+
+### Solus Mate Transition Tool
+
+- Strings which include curly braces `{ }` should be translated leaving the curly braces, *and anything inside the braces*, untouched.
+- Examples:
+  - {DE} Successfully installed, please reboot to continue. **becomes**:
+  - {DE} Instalado exitosamente, reinicie para continuar.
+  - Successfully Installed {} **becomes**
+  - Instalado exitosamente {}
+- Do not translate the following; leave them untouched:
+  - Packagekit
+  - XDG_SESSION_DESKTOP
+