[skip ci] trying ENABLE_CUSTOM_FIRRTL_PASS=1 for Yosys, clarify init script for private tech plugins

docs/VLSI/Advanced-Usage.rst

@@ -3,6 +3,18 @@
 Advanced Usage
 ==============
 
+Hammer Development
+------------------
+If you need to develop Hammer within Chipyard, you will not use the ``hammer-vlsi`` package as installed by conda.
+
+First, clone the `Hammer repository <https://github.com/ucb-bar/hammer>`__ somewhere else on your disk. Then:
+
+.. code-block:: shell
+    
+    pip install -e <path/to/hammer>
+
+Finally, you will need to override the ``site_packages_dir`` variable in ``vlsi/Makefile`` to point to the abspath of your Hammer repository.
+
 Alternative RTL Flows
 ---------------------
 The Make-based build system provided supports using Hammer without using RTL generated by Chipyard. To push a custom Verilog module through, one only needs to append the following environment variables to the ``make buildfile`` command (or edit them directly in the Makefile).