Update release document

HOWTO_RELEASE

@@ -1,13 +1,20 @@
-1. Ensure proper version in package.json 
-2. Ensure NEWS section exists for the new version, review it, add release date
-3. Drop npm-shrinkwrap.json
-4. Run npm install
-5. Test (make check or npm test), fix if broken before proceeding
-6. Run npm shrinkwrap
-7. Set "from" in npm-shrinkwrap.json for known packages
-   (windshaft, node-varnish, grainstore...)
-8. Commit package.json, npm-shrinwrap.json, NEWS
-9. git tag -a Major.Minor.Patch # use NEWS section as content
-10. Announce
-11. Stub NEWS/package for next version
+1. Test (make clean all check), fix if broken before proceeding
+2. Ensure proper version in package.json 
+3. Ensure NEWS section exists for the new version, review it, add release date
+4. Drop npm-shrinkwrap.json
+5. Run npm shrinkwrap to recreate npm-shrinkwrap.json
+6. Commit package.json, npm-shrinwrap.json, NEWS
+7. git tag -a Major.Minor.Patch # use NEWS section as content
+8. Announce on cartodb@googlegroups.com
+9. Stub NEWS/package for next version
 
+Versions:
+
+Bugfix releases increment Patch component of version.
+Feature releases increment Minor and set Patch to zero.
+If backward compatibility is broken, increment Major and
+set to zero Minor and Patch.
+
+Branches named 'b<Major>.<Minor>' are kept for any critical
+fix that might need to be shipped before next feature release
+is ready.