Add tip about lost resources when gathering

Illustration by: Vantha
Feedback by: Vantha, Langbart
Fixes #7652.

binaries/data/mods/public/gui/reference/tips/texts/resource_lost.txt

@@ -0,0 +1,3 @@
+LOST RESOURCES
+Workers cannot carry more than one type of resource at once:
+Order them to drop off their current resources at a dropsite before sending them to a new one.

binaries/data/mods/public/gui/reference/tips/tipfiles.json

@@ -392,6 +392,12 @@
           "persian_architecture.png"
         ]
       },
+      {
+        "textFile": "resource_lost.txt",
+        "imageFiles": [
+          "resource_lost.png"
+        ]
+      },
       {
         "textFile": "select_wounded_units.txt",
         "imageFiles": [