remove XXX from text in faq.md

In several cases where the `faq.md` had **XXX**'s, we replaced the
text with equivalent text for someone to read (such as the **IOCCC
registration procedure** or **IOCCC submit server** is not ready).

In a number of cases, an HTML comment with a **XXX** inside,
was added as an indicator for the need of a future edit.

Added `make sitemap` as an alias for `make gen_sitemap`.

Performed `make gen_top_html sitemap` to do perform the above.

sitemap.xml

@@ -18186,7 +18186,7 @@
 </url>
 <url>
     <loc>https://ioccc-src.github.io/temp-test-ioccc/Makefile</loc>
-    <lastmod>2024-03-10T03:24:01+00:00</lastmod>
+    <lastmod>2024-03-11T05:01:59+00:00</lastmod>
 </url>
 <url>
     <loc>https://ioccc-src.github.io/temp-test-ioccc/README.html</loc>
@@ -19262,11 +19262,11 @@
 </url>
 <url>
     <loc>https://ioccc-src.github.io/temp-test-ioccc/faq.html</loc>
-    <lastmod>2024-03-10T17:01:11+00:00</lastmod>
+    <lastmod>2024-03-11T05:01:02+00:00</lastmod>
 </url>
 <url>
     <loc>https://ioccc-src.github.io/temp-test-ioccc/faq.md</loc>
-    <lastmod>2024-03-09T19:02:12+00:00</lastmod>
+    <lastmod>2024-03-11T05:00:56+00:00</lastmod>
 </url>
 <url>
     <loc>https://ioccc-src.github.io/temp-test-ioccc/inc/README.md</loc>