README: report dependency from libjim

The support for jimtcl submodule is deprecated.
Report libjim as a dependency for building OpenOCD.

Change-Id: Iaaeb03dc810451c0d72add281016c81b8cbf7059
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/8722
Reviewed-by: zapb <dev@zapb.de>
Tested-by: jenkins

Author: borneoa

README

@@ -209,9 +209,7 @@ You'll also need:
 - make
 - libtool
 - pkg-config >= 0.23 or pkgconf
-
-OpenOCD uses jimtcl library; build from git can retrieve jimtcl as git
-submodule.
+- libjim >= 0.79
 
 Additionally, for building from git: