Added steps to creating an in memory instance of the VM

This would be useful when writing an interpreted language where the
"assembly" and the "execution" occur within the same executable.

README.org

@@ -8,9 +8,9 @@ assertions about typing and is very simple to target.
 * How to build
 Requires =GNU make= and a compliant C11 compiler.  Code base has been
 tested against =gcc= and =clang=, but given how the project has been
-written without use of GNU'isms it shouldn't be an issue to compile
+written without use of GNU'isms (that I'm aware of) it shouldn't be an
-using something like =tcc= or another compiler (look at
+issue to compile using something like =tcc= or another compiler (look
-[[file:Makefile::CC=gcc][here]] to change the compiler).
+at [[file:Makefile::CC=gcc][here]] to change the compiler).
 
 To build everything simply run ~make~.  This will build:
 + [[file:lib/inst.c][instruction bytecode system]] which provides
@@ -23,7 +23,7 @@ To build everything simply run ~make~.  This will build:
   how to write compliant assembly.  Also a good test of both the VM
   and assembler.
 
-One may also build each component individually through the
+You may also build each component individually through the
 corresponding recipe:
 + ~make lib~
 + ~make vm~
@@ -33,14 +33,37 @@ corresponding recipe:
 You need to link with the object files for
 [[file:lib/base.c][base.c]], [[file:lib/darr.c][darr.c]] and
 [[file:lib/inst.c][inst.c]] to be able to properly target the OVM.
-The basic idea is to create instructions via ~inst_t~ then using the
+The basic idea is to create some instructions via ~inst_t~,
-~inst(s)_write_*~ API to generate bytecode (and write to a file).
+instantiating a ~prog_t~ structure which wraps those instructions
+(includes a header and other useful things for the runtime), then
+using ~prog_write_file~ to serialise and write bytecode to a file
+pointer.
 
-Then to execute the program, the virtual machine interpreter ~ovm.out~
+To execute directly compiled bytecode use the ~ovm.out~ executable on
-is used.
+the bytecode file.
 
 For clarity, one may build ~lib~ (~make lib~) then use the resulting
 object files to link and create bytecode for the virtual machine.
+** In memory virtual machine
+Instead of serialising and writing bytecode to a file, one may instead
+serialise bytecode in memory using ~prog_write_bytecode~ which writes
+bytecode to a dynamic byte buffer, so called *in memory compilation*.
+To execute this bytecode, deserialise the bytecode into a program then
+load it into a complete ~vm_t~ structure (linking with
+[[file:vm/runtime.c][runtime.c]]).
+
+In fact, you may skip the process of serialising entirely.  You can
+emit a ~prog_t~ structure corresponding to source code, load it
+directly into the ~vm_t~ structure, then execute.  To do so is a bit
+involved, so I recommend looking at [[file:vm/main.c]].  In rough
+steps:
++ Create a virtual machine "from scratch" (load the necessary
+  components (the stack, heap and call stack) by hand)
++ Load program into VM (~vm_load_program~)
++ Run ~vm_execute_all~
+
+This is recommended if writing an interpreted language such as a Lisp,
+where on demand execution of code is more suitable.
 * Lines of code
 #+begin_src sh :results table :exports results
 find -name '*.[ch]' -exec wc -l '{}' ';'