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Fixes spelling in readme.

Co-authored-by: Dan Caseley <dan@caseley.me.uk>

readme.html

@@ -108,7 +108,7 @@ <h3>Storage of data on filesystem</h3>
 
 <table>
     <tr><th>XML property</th> <td><samp>plugin.httpfileupload.serverspecific.fileRepo</samp></td></tr>
-    <tr><th>Property</th> <td><samp>plugin.httpfileupload.fileRepo</samp></td></tr>
+    <tr><th>System Property</th> <td><samp>plugin.httpfileupload.fileRepo</samp></td></tr>
 </table>
 
 <p>
@@ -124,7 +124,7 @@ <h3>Maximum file size</h3>
 
 <table>
     <tr><th>XML property</th> <td><samp>plugin.httpfileupload.serverspecific.maxFileSize</samp></td></tr>
-    <tr><th>Property</th> <td><samp>plugin.httpfileupload.maxFileSize</samp></td></tr>
+    <tr><th>System Property</th> <td><samp>plugin.httpfileupload.maxFileSize</samp></td></tr>
 </table>
 
 <p>
@@ -146,7 +146,7 @@ <h3>Announced web endpoint</h3>
 
 <table>
     <tr><th>XML property</th> <td><samp>plugin.httpfileupload.serverspecific.announcedWebProtocol</samp></td></tr>
-    <tr><th>Property</th> <td><samp>plugin.httpfileupload.announcedWebProtocol</samp></td></tr>
+    <tr><th>System Property</th> <td><samp>plugin.httpfileupload.announcedWebProtocol</samp></td></tr>
 </table>
 
 <p>
@@ -155,15 +155,15 @@ <h3>Announced web endpoint</h3>
 
 <table>
     <tr><th>XML property</th> <td><samp>plugin.httpfileupload.serverspecific.announcedWebHost</samp></td></tr>
-    <tr><th>Property</th> <td><samp>plugin.httpfileupload.announcedWebHost</samp></td></tr>
+    <tr><th>System Property</th> <td><samp>plugin.httpfileupload.announcedWebHost</samp></td></tr>
 </table>
 
 <p>
     To change the HTTP server port from the default value (7443) used by Openfire, use these properties</p>
 
 <table>
     <tr><th>XML property</th> <td><samp>plugin.httpfileupload.serverspecific.announcedWebPort</samp></td></tr>
-    <tr><th>Property</th> <td><samp>plugin.httpfileupload.announcedWebPort</samp></td></tr>
+    <tr><th>System Property</th> <td><samp>plugin.httpfileupload.announcedWebPort</samp></td></tr>
 </table>
 
 <p>
@@ -173,7 +173,7 @@ <h3>Announced web endpoint</h3>
 
 <table>
     <tr><th>XML property</th> <td><samp>plugin.httpfileupload.serverspecific.announcedWebContextRoot</samp></td></tr>
-    <tr><th>Property</th> <td><samp>plugin.httpfileupload.announcedWebContextRoot</samp></td></tr>
+    <tr><th>System Property</th> <td><samp>plugin.httpfileupload.announcedWebContextRoot</samp></td></tr>
 </table>
 
 <h2>When using in an Openfire cluster</h2>
@@ -210,7 +210,7 @@ <h4>Option 1: Each Openfire manages a unique set of data</h4>
 
 <figure>
     <img src="doc-diagram-option-1.png" alt="Diagram illustrating option 1: each Openfire uses it's own data store."/>
-    <figcaption>Diagram illustrating option 1: each Openfire uses it's own data store.</figcaption>
+    <figcaption>Diagram illustrating option 1: each Openfire uses its own data store.</figcaption>
 </figure>
 
 <p>