Fix odd error message in 2020/endoh3/run_clock.sh

When running the script from the shell one would get:

    -bash: ./run_clock.sh: cannot execute: required file not found

and when running from within vim one would get:

    /bin/bash: ./run_clock.sh: /usr/bin/end: bad interpreter: No such file or directory

The problem was that the script had in the shebang /usr/bin/end not
/usr/bin/env.

When I updated the thanks-for-fixes.md file for this I also noted that I
reported to Yusuke in the preview period back in 2020 that in some
systems (it was macOS) due possibly to a timing issue there the script
(which the judges had added) did not work properly with 'make' so Yusuke
changed it to compile the code directly.

2020/endoh3/run_clock.sh

@@ -1,7 +1,8 @@
-#!/usr/bin/end bash
+#!/usr/bin/env bash
+
 while true; do
-cc -std=c11 -Wall -Wextra -pedantic -O3 clock.c -o clock
+    cc -std=c11 -Wall -Wextra -pedantic -O3 clock.c -o clock
-clear
+    clear
-./clock | tee clock.c
+    ./clock | tee clock.c
-sleep 5
+    sleep 5
 done

thanks-for-fixes.md

@@ -2351,6 +2351,39 @@ debugging it since it works with `-O0`.
 He also added the script [demo.sh](2019/karns/demo.sh) to showcase the entry a
 bit more easily.
 
+## [2020/endoh3](2020/endoh3/prog.c) ([README.md](2020/endoh3/README.md))
+
+Cody fixed the script [run_clock.sh](2020/endoh3/run_clock.sh) which gave a
+funny error when running it:
+
+```sh
+$ ./run_clock.sh 
+-bash: ./run_clock.sh: cannot execute: required file not found
+```
+
+If run from within vim a different error message occurred:
+
+```
+/bin/bash: ./run_clock.sh: /usr/bin/end: bad interpreter: No such file or directory
+```
+
+though this was only noticed later on after it was fixed.
+
+What was wrong? A typo in the shebang which had `/usr/bin/end` instead of
+`/usr/bin/env`. Anyone who knows Cody would know that he'd zoom in on that quite
+quick.
+
+Cody also reported (during the preview period of 2020) for some systems (at some
+point?) like macOS the use of `make clock` would not work due possibly to a
+timing issue so Yusuke changed it to compile the [clock.c](2020/endoh3/clock.c)
+file directly (this might have been fixed in the Makefile later on but it
+doesn't hurt to keep it in and this way it isn't a problem in any system). How
+Cody remembers this minor detail more than three years ago is something that
+many people might wonder but he also once told us that if someone moves
+something of his even a millimetre from where it was he knows it so he might be
+called unusual (and he argues, with pride, eccentric :-) ) :-)
+
+
 ## [2020/ferguson2](2020/ferguson1/prog.c) ([README.md](2020/ferguson1/README.md))
 
 Cody, with intentional irony here :-), fixed formatting, links and typos in