Add a README to the src directory

src/README.md

@@ -0,0 +1,32 @@
+# SpacemanDMM`/src`
+
+SpacemanDMM consists of several packages. Each may be built by running
+`cargo build -p <name>` from the repository root. If no `-p` flag is
+specified, all packages will be built. Adding `--release` will enable more
+optimization flags, taking longer to compile but producing faster executables.
+
+```text
+dreammaker ←- dm-langserver
+    ↑
+dmm-tools ←- cli
+    ↑
+spaceman-dmm -→ qt-extras
+```
+
+* [dreammaker](dreammaker/) - a pure-Rust parsing suite for the DreamMaker
+  programming language.
+
+* [dm-langserver](langserver/) - a [language server] based upon that parser.
+
+* [dmm-tools](tools/) - additional libraries for working with DreamMaker icon
+  and map files, including a renderer.
+
+* [cli](cli/) - the command-line interface to `dmm-tools`.
+
+* [qt-extras](qt-extras/) - additional integrations between Rust and Qt for
+  use by the editor.
+
+* [spaceman-dmm](editor/) - a very early prototype of a map editor meant as an
+  alternative to DreamMaker's default.
+
+[language server]: https://langserver.org/