Introductory text and hello world for Maclisp.

doc/hello-lisp.md

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+# Introduction to Maclisp
+
+### A "hello world" example
+
+Lisp programs can be developed in the interpreter, but serious
+applications will usually be compiled and saved as standalone
+executable programs.
+
+Enter this small program and save it as `hello lisp`.  Then compile it
+with the command `:complr hello lisp`.  Now the compiled code will be
+in the file `hello fasl`.
+
+```
+(defun hello ()
+  (princ "Hello Maclisp!")
+  (terpri)
+  (quit))
+```
+
+To make the executable program, enter this code (comments are
+optional) and save it as `hello dumper`.  Then run the command `:lisp
+hello dumper`.  The result will be that Maclisp loads the `hello fasl`
+file and writes out `ts hello`.
+
+```
+(comment)                             ;Avoid question about allocation.
+(progn
+  (close (prog1 infile (inpush -1)))  ;Make sure file channels are closed.
+  (fasload hello)                     ;Load the compiled program.
+  (gc)                                ;Garbage collect.
+  (purify 0 0 'bporg)                 ;Purify memory pages.
+  (sstatus flush t)                   ;Share pure pages with Maclisp.
+  (suspend ":kill " '(ts hello))      ;Save image as an executable program.
+  (hello))                            ;Executable program will start from here.
+```