clarify that left/right meant to be given relative to the cyclist

see https://github.com/openstreetmap/iD/issues/10128
see https://wiki.openstreetmap.org/w/index.php?title=Tag:highway%3Dcyclist_waiting_aid&oldid=2631832
see https://community.openstreetmap.org/t/approved-feature-proposal-cyclist-footrests-and-handrails-cyclist-waiting-aid/105762/3

data/fields/side.json

@@ -4,8 +4,8 @@
     "label": "Side",
     "strings": {
         "options": {
-            "left": "Left",
-            "right": "Right"
+            "left": "Left of Cyclist",
+            "right": "Right of Cyclist"
         }
     },
     "autoSuggestions": false

interim/source_strings.yaml

@@ -4809,9 +4809,9 @@ en:
         label: Side
         options:
           # side=left
-          left: Left
+          left: Left of Cyclist
           # side=right
-          right: Right
+          right: Right of Cyclist
       siren/purpose:
         # siren:purpose=*
         label: Purpose