[docs] Tell users to source env.sh in quick start

docs/Quick-Start.rst

@@ -28,6 +28,11 @@ To build the toolchains, you should run:
 .. Note:: If you are planning to use the Hwacha vector unit, or other RoCC-based accelerators, you should build the esp-tools toolchains by adding the ``esp-tools`` argument to the script above.
   If you are running on an Amazon Web Services EC2 instance, intending to use FireSim, you can also use the ``--ec2fast`` flag for an expedited installation of a pre-compiled toolchain.
 
+Finally, set up Chipyard environment varibles and put the newly built toolchain on your path:
+
+.. code-block:: shell
+
+    source ./env.sh
 
 What's Next?
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