…k#195)

This expands the build instructions to mention a few things previously
missing, including the need to set JULIA_PATH and to check out the 'dev'
branch. Without the latter, you will get a working Julia but it is not
MMTk-enabled.

I also tried to eliminate a bit of duplication, have the "quick build"
instructions be a sequence of verbatim shell commands that Should Work
(tested working for me) and put them first.

…#193)

Merge with mmtk/julia#72.

Should add info to Julia's banner about the version of MMTk used in the
build such as:

```
               _
   _       _ _(_)_     |  Documentation: https://docs.julialang.org
  (_)     | (_) (_)    |
   _ _   _| |_  __ _   |  Type "?" for help, "]?" for Pkg help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 1.12.0-DEV.955 (2024-11-26)
 _/ |\__'_|_|_|\__'_|  |  adding-tag-to-banner/0ccc307863* (fork: 101 commits, 134 days)
|__/                   |  Built with MMTk Julia 0.1.0 (a775934-dirty), using MMTk 0.27.0 (de10fa4, DEFAULT, IMMIX_NON_MOVING, IMMIX_SMALLER_BLOCK, OBJECT_PINNING, VM_SPACE)
```