updated README to describe changes in version 3.3 [ci skip]

README.md

@@ -41,6 +41,20 @@ believe it's correct.
 For help with installing LOOS, please see the [INSTALL.md](INSTALL.md) file.  For
 more details about what has changed in LOOS, see the [ChangeLog](ChangeLog) file.
 
+### Release 3.3.0
+
+This release has a new and improved facility for reweighting (from Louis Smith), methods for calculating logistic and hard-cutoff lateral densities in AtomicGroup, several new tools for working with clusters in the Clustering package, and dipole computation in membrane_map.
+
+There are also a number of bugfixes:
+ - Incorrect bonds removed from add_molecule.py
+ - Fixed units for periodic box read by gmxdump2pdb.pl
+ - Update to handle new constraints format in gromacs 2020.3+ in gmxdump2pdb.pl
+ - Fixed charge units when reading Amber prmtop files
+ - OMG correctly handles 4- and 5-site water models
+ - In subsetter and merge-traj, the --regex and --scanf flags now imply --sort
+
+ There were also a few housekeeping updates. We migrated continuous integration from Travis-CI to GitHub Actions, Louis Smith contributed a *much* cleaner .gitignore file, and we fixed a potential build-bug where the C++ file generated by swig had different names depending on which compiler/swig version was used. We also added scikit-learn to the list of conda packages installed by conda_build.sh, and fixed a silly bug in its detection of the available compilers.
+
 ### Release 3.1.0
 
 This is another major release. The biggest change is a totally reworked build