changelog: added to account for breaking changes

CHANGELOG.md

+# go-ipfs changelog
+
+Until we near full stability, this changelog must only
+list breakages and backwards incompatible changes.
+
+
+### 2015-01-31:
+
+* bootstrap addresses now have .../ipfs/... in format
+  config file Bootstrap field changed accordingly. users
+  can upgrade cleanly with:
+
+      ipfs bootstrap >boostrap_peers
+      ipfs bootstrap rm --all
+      <install new ipfs>
+      <manually add .../ipfs/... to addrs in bootstrap_peers>
+      ipfs bootstrap add <bootstrap_peers