Minor updates to the docs

docs/index.txt

@@ -9,6 +9,7 @@ Welcome to tupak's documentation!
    :caption: Contents:
 
    likelihood
+   samplers
 
 
 Indices and tables

docs/likelihood.txt

@@ -2,7 +2,29 @@
 Likelihood
 ==========
 
-.. automodule:: tupak.likelihood
+`tupak` likelihood objects are used in calculating the likelihood of the data
+for some specific set of parameters. In mathematical notation, the likelihood
+can be generically written as :math:`\mathcal{L}(d| \theta)`. How this is
+coded up will depend on the problem, but `tupak` expects all likelihood
+objects to have a `parameters` attribute (a dictionary of key-value pairs) and
+a `log_likelihood()` method.
+
+The default likelihood we use in the examples is `GravitationalWaveTransient`:
+
+.. autoclass:: tupak.likelihood.GravitationalWaveTransient
+    :members:
+
+We also provide a simpler likelihood
+
+.. autoclass:: tupak.likelihood.BasicGravitationalWaveTransient
     :members:
 
+We provide an empty parent class which can be subclassed for alternative use
+cases
+
+.. autoclass:: tupak.likelihood.Likelihood
+    :members:
+
+
+