Mended broken links in README.html

Mended some broken relative links in README.html that
pointed to other parts of the docs.

Also, rename "Mac OS X" to "macOS" in more places.

docs/en/html/EXTENDING.html

@@ -355,7 +355,7 @@
         </blockquote>
 
         <h4>
-          Mac OS X
+          macOS
         </h4>
 
         <blockquote>
@@ -1471,7 +1471,7 @@
       <p>
         A graphical tool, called <i><b>poEdit</b></i> (<a href=
         "http://www.poedit.net/">http://www.poedit.net/</a>), is
-        available for Linux, Windows and Mac&nbsp;OS&nbsp;X.
+        available for Linux, Windows and macOS.
       </p>
 
       <p>

docs/en/html/FAQ.html

@@ -538,7 +538,7 @@
           </dd>
 
           <dt>
-            Mac OS X
+            macOS
           </dt>
 
           <dd>

docs/en/html/OPTIONS.html

@@ -115,7 +115,7 @@
       </blockquote>
 
       <h2>
-        Mac&nbsp;OS&nbsp;X Users
+        macOS Users
       </h2>
 
       <blockquote>
@@ -389,7 +389,7 @@
             the <b>[Alt]</b> modifier key is being held. (This is
             typically used for providing a print dialog, similar to
             when pressing <b>[Alt]</b>+'Print' in Windows and
-            Mac&nbsp;OS&nbsp;X.)
+            macOS.)
           </p>
 
           <p>

docs/en/html/README.html

@@ -2093,24 +2093,24 @@
       "<code>docs</code>" folder/directory) include:
       <ul>
         <li>
-          <a href="../magic-docs/html/">"Magic" Tool Documentation
+          <a href="../magic-docs/html/index.html">"Magic" Tool Documentation
           ("magic-docs")</a><br>
           Documentation for each of the currently-installed "Magic"
           tools.
         </li>
 
         <li>
-          <a href="../AUTHORS.txt">AUTHORS.txt</a><br>
+          <a href="../../AUTHORS.txt">AUTHORS.txt</a><br>
           List of authors and contributors.
         </li>
 
         <li>
-          <a href="../CHANGES.txt">CHANGES.txt</a><br>
+          <a href="../../CHANGES.txt">CHANGES.txt</a><br>
           Summary of changed between releases.
         </li>
 
         <li>
-          <a href="../COPYING.txt">COPYING.txt</a><br>
+          <a href="../../COPYING.txt">COPYING.txt</a><br>
           Copying license (The GNU General Public License).
         </li>