[doc] #5: document how to build with Pyinstaller.

README.md

@@ -6,6 +6,7 @@
 ## Install
 - [Install inside a Python environemnt](https://github.com/duniter/silkaj/blob/master/doc/install_pyenv.md)
 - [Install without Python environment](https://github.com/duniter/silkaj/blob/master/doc/install_on_the_system.md)
+- [Build an executable with Pyinstaller](https://github.com/duniter/silkaj/blob/master/doc/build_with_pyinstaller.md)
 - [Install as a drop-down for GNOME Shell with Argos](https://github.com/duniter/silkaj/blob/master/doc/argos.md)
 
 ## Usage

doc/build_with_pyinstaller.md

+# Build with Pyinstaller
+
+## Install Pyinstaller
+```bash
+pip install pyinstaller
+```
+
+If you are using Pyenv, don’t forget to save pyinstaller install:
+```bash
+pyenv rehash
+```
+
+## Build
+```bash
+pyinstaller src/silkaj.py --hidden-import=_cffi_backend --hidden-import=_scrypt --onefile
+```
+
+You will found the exetuable file on `silkaj/dist` folder.