Update readme

README.md

@@ -15,11 +15,11 @@ decent platforms; I use it on macOS and have tested it on Linux.
 
 Everything else is downloaded into the Docker container.
 
-## How to build and flash
+## How to do stuff
 
-- Using Docker:
-    - `make` — full build. Will create the docker container (expect 10-30min)
-      if needed.
+- Building in Docker:
+    - `make` (`make all`) — full build. Will create the docker image
+      (expect 10-30min) if needed.
     - `make wipe` — full clean and rebuild.
 - Building locally, if you have your own toolchain already:
     - `make lall` ("local all")
@@ -30,7 +30,7 @@ Everything else is downloaded into the Docker container.
 `make flash` expects to find a WCH-compatible patched openocd on the system
 PATH. If yours lives elsewhere, define `OPENOCD_DIR` on the environment.
 
-## Using gdb
+### Using gdb
 
 The Docker container has gdb too. To debug, first launch openocd:
 
@@ -51,6 +51,10 @@ to openocd.
 As above, if you're not using Docker, `make lgdb` will launch gdb locally,
 also automatically loading the firmware and connecting.
 
+### Miscellaneous
+
+- `make shell` will open a shell in Docker.
+
 ## What's in here?
 
 The directory tree contains: