Add README

Makefile

@@ -1,4 +1,4 @@
-TESTS=GCBench MT_GCBench MT_GCBench2
+TESTS=GCBench # MT_GCBench MT_GCBench2
 COLLECTORS=bdw semi
 
 CC=gcc

README.md

@@ -0,0 +1,35 @@
+# GC workbench
+
+This repository is a workbench for implementing different GCs.  It's a
+scratch space.
+
+## License
+
+GCBench.c, MT_GCBench.c, and MT_GCBench2.c are from
+https://hboehm.info/gc/gc_bench/ and have a somewhat unclear license.  I
+have modified GCBench significantly so that I can slot in different GC
+implementations.  The GC implementations themselves are available under
+a MIT-style license, the text of which follows:
+
+```
+Copyright (c) 2022 Andy Wingo
+
+Permission is hereby granted, free of charge, to any person obtaining a
+copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be included
+in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+```