README: indicate default branch is not used

There has been a commit history on the dpdk-stable repo
default branch even though it is not actively used or really
defined what should be there. This is the default branch when
cloning the repo so it can be confusing.

Drop all history on dpdk-stable repo default branch back to the
initial commit and add to the existing README blurb that
stable/LTS branches should be used.

Signed-off-by: Kevin Traynor <[email protected]>
Acked-by: Luca Boccassi <[email protected]>
Acked-by: David Marchand <[email protected]>
Acked-by: Thomas Monjalon <[email protected]>

Author: kevintraynor

README

@@ -0,0 +1,18 @@
+DPDK is a set of libraries and drivers for fast packet processing.
+
+The DPDK uses the Open Source BSD-3-Clause license for the core libraries
+and drivers. The kernel components are GPL-2.0 licensed.
+
+Documentation is available at: https://core.dpdk.org/doc/
+
+For questions and usage discussions, subscribe to: [email protected]
+Report bugs and issues to the development mailing list: [email protected]
+
+This is the default branch of the dpdk-stable repo. It is unused.
+Please switch branch to one of the stable/LTS branches.
+
+Details of currently maintained stable/LTS branches are available at:
+https://core.dpdk.org/roadmap/#stable
+
+Releases from current and previously maintained stable/LTS branches
+are available via git tags or at: https://core.dpdk.org/download/