Updated website documentation.

website/README.md

+# Website content
 The content of this directory is published
 [here](https://humgenprojects.lumc.nl/trac/humgenprojects/wiki/NGS-intro).
+
+## Updating the website
+We use the [tracwiki](https://pypi.python.org/pypi/tracwiki) program to
+communicate with the Trac server.
+
+### Preparations
+Install tracwiki:
+
+    pip install tracwiki
+
+Configuration will make a file named **.trac_config**. Do not add this file to
+the git repository.
+
+    tracwiki config https://humgenprojects.lumc.nl/trac/humgenprojects
+
+### Updating and attaching
+Before making changes, make sure you have the last version:
+
+    tracwiki checkout NGS-intro
+
+Edit the file and synchronise with the server:
+
+    tracwiki commit
+
+Attaching files (updating attached files):
+
+    tracwiki attach NGS-intro mypresentation.pdf