updates READMEs re electrum-ecc

README.md

@@ -23,29 +23,37 @@ is a TL;DR:
 
 ```
 $ sudo apt-get install libsecp256k1-dev
-$ python3 -m pip install --user ".[gui,crypto]"
+$ ELECTRUM_ECC_DONT_COMPILE=1 python3 -m pip install --user ".[gui,crypto]"
 ```
 
 ### Not pure-python dependencies
 
+#### Qt GUI
+
 If you want to use the Qt interface, install the Qt dependencies:
 ```
 $ sudo apt-get install python3-pyqt6
 ```
 
+#### libsecp256k1
+
 For elliptic curve operations,
 [libsecp256k1](https://github.com/bitcoin-core/secp256k1)
-is a required dependency:
+is a required dependency.
+
+If you "pip install" Electrum, by default libsecp will get compiled locally,
+as part of the `electrum-ecc` dependency. This can be opted-out of,
+by setting the `ELECTRUM_ECC_DONT_COMPILE=1` environment variable.
+For the compilation to work, besides a C compiler, you need at least:
+```
+$ sudo apt-get install automake libtool
+```
+If you opt out of the compilation, you need to provide libsecp in another way, e.g.:
 ```
 $ sudo apt-get install libsecp256k1-dev
 ```
 
-Alternatively, when running from a cloned repository, a script is provided to build
-libsecp256k1 yourself:
-```
-$ sudo apt-get install automake libtool
-$ ./contrib/make_libsecp256k1.sh
-```
+#### cryptography
 
 Due to the need for fast symmetric ciphers,
 [cryptography](https://github.com/pyca/cryptography) is required.
@@ -54,6 +62,8 @@ Install from your package manager (or from pip):
 $ sudo apt-get install python3-cryptography
 ```
 
+#### hardware-wallet support
+
 If you would like hardware wallet support,
 [see this](https://github.com/spesmilo/electrum-docs/blob/master/hardware-linux.rst).