Really spell out the last of the required UNIX utilities.

Finishing the job started in Pull Request #4301

<https://github.com/fish-shell/fish-shell/pull/4301>

Thanks to @faho for filtering and sorting my giant list of detected
possible commands.

<https://github.com/fish-shell/fish-shell/issues/2062#issuecomment-321788080>

README.md

@@ -21,7 +21,21 @@ fish depends on a curses implementation, such as ncurses. The headers and librar
 
 fish requires PCRE2 due to the regular expression support contained in the `string` builtin. A copy is included with the source code, and will be used automatically if it does not already exist on your system.
 
-fish requires gettext for translation support.
+* a curses implementation such as ncurses (which should provide the `tput` command).
+* gettext, if you need the localizations.
+* PCRE2, due to the regular expression support contained in the `string` builtin. A copy is included with the source code, and will be used automatically if it does not already exist on your system.
+* a number of common UNIX utilities:
+    * an awk implementation, such as gawk, mawk, etc
+    * coreutils --- at least basename, cat, cut, date, dircolors, dirname, ls, mkdir, mkfifo, mktemp, rm, seq, sort, stat, stty, tail, tr, tty, uname, uniq, wc, whoami
+    * find
+    * getent (part of glibc)
+    * getopt
+    * grep
+    * hostname
+    * kill
+    * ps
+    * sed
+* bc, the "basic calculator" program.
 
 Building the documentation requires Doxygen 1.8.7 or newer.