Add docs on share plugin (#5331)

…and mention it in the "sharing tiddlers" tiddler

editions/tw5.com/tiddlers/plugins/Share Plugin.tid

@@ -0,0 +1,12 @@
+created: 20201228143125000
+modified: 20201228143125000
+tags: OfficialPlugins
+title: Share Plugin
+type: text/vnd.tiddlywiki
+
+<div class="tc-message-box">Do not install this plugin unless you understand exactly what it does</div>
+
+This experimental plugin provides tools to share tiddlers via URLs, comprising:
+
+* The ability to load a group of tiddlers from the browser location hash at startup
+* Wizard and templates to create URLs from group of tiddlers

editions/tw5.com/tiddlers/workingwithtw/Sharing your tiddlers with others.tid

@@ -1,5 +1,5 @@
 created: 20140908163900000
-modified: 20170328142732658
+modified: 20201228143412000
 tags: Learning
 title: Sharing your tiddlers with others
 type: text/vnd.tiddlywiki
@@ -14,3 +14,4 @@ There are a number of ways that you can share [[tiddlers|Tiddlers]] or your whol
 * You can [[share a Dropbox link to your TiddlyWiki|Sharing a TiddlyWiki on Dropbox]]
 * You can [[export tiddlers|How to export tiddlers]] (<<.icon $:/core/images/export-button>>) in a variety of formats including text, static HTML and comma separated values (ie spreadsheet compatible)
 *You can also share tiddlers merely by making your ~TiddlyWiki accessible to others, for example by publishing it online, so that they can [[import tiddlers|Importing Tiddlers]] from it
+* There is an experimental [[sharing plugin|Share Plugin]] that you can use to share tiddlers via the URL location hash.