README: fix link to install section

The anchor names generated by readthedocs.io are all lower-case.

Signed-off-by: Bastian Krause <bst@pengutronix.de>

Author: Bastian-Krause

README.rst

@@ -63,7 +63,7 @@ and is currently in active use and development.
 Quickstart
 ----------
 See the `Installation section
-<http://labgrid.readthedocs.io/en/latest/getting_started.html#Installation>`_
+<http://labgrid.readthedocs.io/en/latest/getting_started.html#installation>`_
 for more details.
 
 Clone the git repository: