Add note to explain how to manually install PyQt to virtualenv

This comment was formerly housed at another repo, which has now
been made inactive and the comment was removed. Note that this
manual process will be superceded soon by a change to the
installation script.

README.md

@@ -39,7 +39,13 @@ If you are not new to Joinmarket, the notes in the [scripts readme](scripts/READ
 Provides single join and multi-join/tumbler functionality (i.e. "Taker") only, in a GUI.
 
 Binaries that are built and signed will be in the Releases page. To run the script
-`joinmarket-qt.py` from the command line, pay attention to the note [here](https://github.com/AdamISZ/electrum-joinmarket-plugin#a-note-on-pyqt4-and-virtualenv).
+`joinmarket-qt.py` from the command line, the following extra manual step is unfortunately necessary:
+
+PyQt doesn't play nice with virtualenvs; to use it, as required here, you can copy the files from your system Python installation into the virtualenv:
+
+Copy the directory `PyQt4`, the files `sip*.so`, `sipconfig.py` and `sipconfig_nd.py` from the
+system level `dist-packages` (usually `/usr/lib/python2.7/dist-packages` to the virtualenv `site-packages` directory (usually `/home/user/joinmarket-clientserver/jmvenv/lib/python2.7/site-packages`).
+ Afterwards, be sure to reactivate the virtualenv (use `deactivate` and `source jmvenv/bin/activate`). Then the command `python joinmarket-qt.py` from within the `scripts` subdirectory should work. There is a [walkthrough](docs/JOINMARKET-QT-GUIDE.md) for what to do next.
 
 ### Notes on architectural changes (can be ignored)