Add docs for list-thumbnails macro

Thanks @Marxsal

editions/tw5.com/tiddlers/macros/examples/list-thumbnails Macro (Examples).tid

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+created: 20200612170734735
+modified: 20200612171403882
+tags: [[Macro Examples]]
+title: list-thumbnails Macro (Examples)
+type: text/vnd.tiddlywiki
+
+This example lists all the tiddlers which are tagged with "HelloThumbnail":
+
+<$macrocall $name=".example" n="1" eg="""<<list-thumbnails filter:"[tag[HelloThumbnail]]" width:"168" height:"95">>"""/>
+
+

editions/tw5.com/tiddlers/macros/list-thumbnails Macro.tid

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+caption: thumbnail
+created: 20200612170158838
+modified: 20200612171804473
+tags: Macros [[Core Macros]]
+title: list-thumbnails Macro
+type: text/vnd.tiddlywiki
+
+The <<.def list-thumbnails>> [[macros|Macros]] are used to create lists of linkable thumbnail panels.
+
+!! Parameters
+
+;filter
+: filter for selecting thumbnails
+;width
+:Width of thumbnail (default 280 pixels)
+;height
+:Height of thumbnail (default 157 pixels)
+
+<<.macro-examples "list-thumbnails">>