Allow multiple shells to be enabled.

README

@@ -51,6 +51,38 @@ Supported kernels:
 
 ----------------
 
+Shells:
+
+lash is the very smallest shell (adds just 10k) and it is quite usable as 
+a command prompt, but it is not suitable for any but the most trivial
+scripting (such as an initrd that calls insmod a few times) since it does
+not understand Bourne shell grammer.  It does handle pipes, redirects, and
+job control though.  Adding in command editing makes it very nice
+lightweight command prompt.
+
+hush is also quite small (just 18k) and it has very complete Bourne shell
+grammer.  It handles if/then/else/fi just fine, but doesn't handle loops
+like for/do/done or case/esac and such.  It also currently has a problem
+with job control.
+
+msh: The minix shell (adds just 30k) is quite complete and handles things
+like for/do/done, case/esac and all the things you expect a Bourne shell to
+do.  It is not always pedantically correct about Bourne shell grammer (try
+running the shell testscript "tests/sh.testcases" on it and compare vs bash)
+but for most things it works quite well.  It also uses only vfork, so it can
+be used on uClinux systems.  This was only recently added, so there is still
+room to shrink it further...
+
+ash: This adds about 60k in the default configuration and is the most
+complete and most pedantically correct shell included with busybox.  This
+shell was also recently added, and several people (mainly Vladimir and Erik)
+have been working on it.  There are a number of configurable things at the
+top of ash.c as well, so check those out if you want to tweak things.  The
+Posix math support is currently disabled (that bit of code was horrible) but
+will be restored for the next BusyBox release.
+
+----------------
+
 Getting help:
 
 When you find you need help, you can check out the BusyBox mailing list