Update README and HISTORY with changes

HISTORY.txt

@@ -1,11 +1,16 @@
 Changelog
 =========
 
-0.12.4 (unreleased)
+0.12.5 (unreleased)
 -------------------
 
 - Nothing changed yet.
 
+0.12.4 (2020-02-28)
+-------------------
+
+- Add option to set context via environment variable or configuration file.
+
 
 0.12.3 (2019-12-03)
 -------------------

README.rst

@@ -21,11 +21,18 @@ Example usage:
         ipdb.set_trace()
         ipdb.set_trace(context=5)  # will show five lines of code
                                    # instead of the default three lines
+                                   # or you can set it via IPDB_CONTEXT_SIZE env variable
+                                   # or setup.cfg file
         ipdb.pm()
         ipdb.run('x[0] = 3')
         result = ipdb.runcall(function, arg0, arg1, kwarg='foo')
         result = ipdb.runeval('f(1,2) - 3')
 
+It's possible to set up context using a `.ipdb` file on your home folder or `setup.cfg`
+on your project folder. You can also set your file location via env var `$IPDB_CONFIG`.
+Your environment variable has priority over the home configuration file,
+which in turn has priority over the setup config file.
+
 The post-mortem function, ``ipdb.pm()``, is equivalent to the magic function
 ``%debug``.