Update README.md

Author: ntessore

README.md

@@ -2,23 +2,50 @@
 transformcl
 ===========
 
-**transform angular power spectra and correlation functions**
+**Transform angular power spectra and correlation functions.**
 
 This is a minimal Python package for transformations between angular power
-spectra and correlation functions.  It is currently limited to the zero spin
+spectra and correlation functions.  It is currently limited to the spin zero
 case.
 
 The package can be installed using pip:
 
     pip install transformcl
 
-Then import the `cltocorr` and `corrtocl` functions from the package:
+Then import the package to use the functions:
 
-    from transformcl import cltocorr, corrtocl
+```py
+import transformcl
+t = transformcl.theta(cl.size)
+ct = transformcl.corr(cl)
+```
 
 For more information, please see the [documentation].
 
 Current functionality covers the absolutely minimal use case.  Please open an
 issue on GitHub if you would like to see anything added.
 
-[documentation]: https://cltools.readthedocs.io/transformcl/
+[documentation]: https://glass.readthedocs.io/projects/transformcl/latest
+
+
+Backends
+--------
+The `transformcl` package supports multiple transform backends.  The
+current backend can be changed globally by assigning to
+`transformcl.backend`:
+
+```py
+transformcl.backend = "<choice>"
+...
+```
+
+or using the `transformcl.use()` context manager:
+
+```py
+with transformcl.use("<choice>"):
+    ...
+```
+
+The list of available backends can be found in the [documentation][backends].
+
+[backends]: https://glass.readthedocs.io/projects/transformcl/latest#backends