Add note about validity of node times & tsdate

Author: hyanwong

README.md

@@ -13,3 +13,7 @@ The algorithm, its rationale, and results from testing on simulated and real dat
 
 Please cite this if you use ``tsinfer`` in your work. Code to reproduce the results in the paper is present in a [separate GitHub repository](https://github.com/mcveanlab/treeseq-inference).
 
+Note that `tsinfer` does not attempt to infer node times (i.e. branch lengths of the
+inferred trees). If you require a tree sequence where the dates of common ancestors
+are expressed in calendar or generation times, you should post-process the ``tsinfer``
+output using software such as [``tsdate``](https://github.com/tskit-dev/tsdate).

docs/introduction.rst

@@ -20,3 +20,13 @@ The output of ``tsinfer`` is a :class:`tskit.TreeSequence` and so the
 full `tskit API <https://tskit.readthedocs.io>`_ can be used to
 analyse real data, in precisely the same way that it is commonly used
 to analyse simulation data, for example, from `msprime <https://msprime.readthedocs.io/>`_.
+
+.. note::
+
+  ``Tsinfer`` infers the genetic relationships between sampled genomes, but does not
+  attempt to infer the *times* of most recent common ancestors (tMRCAs) in the genealogy.
+  If you are using the output of ``tsinfer`` in downstream analysis that relies on
+  node times, you are advised not to use the inferred tree sequences directly; instead,
+  you should post-process the ``tsinfer`` output using software such as
+  `tsdate <https://tsdate.readthedocs.io>`_ that attempts to assign calendar or
+  generation times to the tree sequence nodes.