[deps] Remove old deps scripts and update deps README as README.md (#391)

Signed-off-by: Geoff Gustafson <[email protected]>

Author: grgustaf

deps/README

@@ -0,0 +1,24 @@
+ZJS Dependencies
+================
+
+This directory contains projects that the ZJS work depends on so we can
+maintain our own patches to them when necessary.
+
+Now we use git submodules to maintain these dependencies, so the old scripts
+that were here have been removed. Use `make update` to sync the dependencies
+to the commits they are supposed to be on given the version of ZJS you have
+checked out. This update target runs automatically when you build normally.
+
+To update the commit for a dependency directory, change to the `deps`
+subdirectory and check out the desired commit. Then when you look at your
+`git diff` back at the root level, you will see the change and can commit it.
+
+For example:
+
+```bash
+$ cd deps/zephyr
+$ git checkout v1.6.0
+$ cd ../..
+$ git add deps/zephyr
+$ git commit
+```