add readme

Author: 3b

README.md

@@ -0,0 +1,22 @@
+Official dockerfile includes a quicklisp install with the following
+installed: `drakma alexandria split-sequence serapeum esrap cl-ppcre
+babel flexi-streams closer-mop cffi ironclad opticl cl-wav` (see
+https://github.com/icfpcontest2020/dockerfiles/blob/master/dockerfiles/commonlisp/Dockerfile.base#L26
+for current list, and send pull requests to make additions if you
+think anything particularly common was missed). Those are mostly just
+for convenience and to save a bit of build time, and you can include
+your own `quicklisp/` dir in your solution repo and it will be copied
+over the existing one.
+
+`app/` is added to `ql:*local-project-directories*`, so `.asd` files
+there should be found by ql. By default `build.sh` loads the
+`icfp2020-starterkit-cl` system, modify that as needed.
+
+Alternately, you can modify `build.sh` as desired to build from the
+contents of your submission repo as you see fit (no network access
+allowed during build or run, so any extra dependencies must be
+included in submission repo or added to the main dockerfile before the
+contest, send pull requests to
+https://github.com/icfpcontest2020/dockerfiles). See
+https://github.com/icfpcontest2020/dockerfiles/blob/master/README.md
+for full details of how submission works.