Minor fixes in bin/README.md

A few typos were fixed.

One tool had the description reworded a bit to make it (hopefully) a bit
clearer.

A link was fixed but I am not sure if, since it's a script, it should
link to the GitHub repo or not, like with other markdown files. I
changed it to use the %%var%% that the bin/README.md file uses. This is
one reason links have not been checked. The other reason is I have not
gone through the entire file yet.

I notice some tools do not have example usage and those could be added
too.

There was an apparent typo in bin/find-missing-links.sh and this same
typo was fixed in bin/README.md. I am not sure exactly what was meant,
however, so it might need further modifications.

I have (the caveats above notwithstanding) gone up through
pandoc-wrapper.sh or just before it.

Regenerated bin/index.html.

bin/find-missing-links.sh

@@ -4,10 +4,10 @@
 #
 # Find all markdown links to local files that do not exist.
 #
-# This tool does **NOT** check of a remote URL exists.
+# This tool does **NOT** check that a remote URL exists.
 # This tool only checks on links to local files.
 #
-# This tool does **NOT** check links into a given place in a file.
+# This tool does **NOT** check links in a given place in a file.
 # This tool only checks that local files linked by markdown exist.
 #
 # This tool does **NOT** check HTML file links.