update README to mention libsecp

README.rst

@@ -26,11 +26,28 @@ Electrum - Lightweight Bitcoin client
 Getting started
 ===============
 
-Electrum is a pure python application. If you want to use the
-Qt interface, install the Qt dependencies::
+Electrum itself is pure Python, and so are most of the required dependencies.
+
+Non-python dependencies
+-----------------------
+
+If you want to use the Qt interface, install the Qt dependencies::
 
     sudo apt-get install python3-pyqt5
 
+For elliptic curve operations, libsecp256k1 is a required dependency::
+
+    sudo apt-get install libsecp256k1-0
+
+Alternatively, when running from a cloned repository, a script is provided to build
+libsecp256k1 yourself::
+
+    ./contrib/make_libsecp256k1.sh
+
+
+Running from tar.gz
+-------------------
+
 If you downloaded the official package (tar.gz), you can run
 Electrum from its root directory without installing it on your
 system; all the python dependencies are included in the 'packages'
@@ -40,22 +57,19 @@ directory. To run Electrum from its root directory, just do::
 
 You can also install Electrum on your system, by running this command::
 
-    sudo apt-get install python3-setuptools
-    python3 -m pip install .[fast]
+    sudo apt-get install python3-setuptools python3-pip
+    python3 -m pip install --user .
 
 This will download and install the Python dependencies used by
 Electrum instead of using the 'packages' directory.
-The 'fast' extra contains some optional dependencies that we think
-are often useful but they are not strictly needed.
 
 If you cloned the git repository, you need to compile extra files
 before you can run Electrum. Read the next section, "Development
-Version".
-
+version".
 
 
 Development version
-===================
+-------------------
 
 Check out the code from GitHub::
 
@@ -65,7 +79,7 @@ Check out the code from GitHub::
 
 Run install (this should install dependencies)::
 
-    python3 -m pip install .[fast]
+    python3 -m pip install --user .
 
 
 Compile the protobuf description file::