Add contributing section in DEVELOPERS

Add new makefile command: devenvironment.

DEVELOPERS.md

@@ -2,7 +2,13 @@
 
 [![Ballmer "developers!"](https://passh.hackan.net/img/developers.png)](http://www.youtube.com/watch?v=V-FkalybggA "Developers")
 
-This guide is intended for developers that want to implement **Passphrase** in their projects.
+This guide is intended for developers that want to implement **Passphrase** in their projects or that want to contribute to this project.
+
+## Contributing
+
+If you want to develope or contribute to this project, you can quickly start by issuing `make devenvironment`: it creates a virtualenv directory and installs requirements and the *Passphrase* package. This is, of course, not mandatory.
+
+Every contribution must be acompanied by it's tests. As a general guideline, follow PEP8 (flake8 must run without warnings) and prefer Exceptions over assumptions. Try hard on not to add dependencies: I'm going to reject PRs with external dependencies that are not entirely justified (and for this project in particular, having 0 dependencies is very important).
 
 ## About the package
 
@@ -27,7 +33,9 @@ my_async_sleep(pause_sec(1, 5))
 
 Of course, you can't just pause the whole server, or let the user hanging there for some seconds... or maybe, you can. I let you decide how to solve it. Another, even better, way to solve this is to provide the system for a secure external random source, such as a randomness generator like Chaoskey.
 
-## Requirements
+If you are using a Linux OS, you can use `Aux::system_entropy()` to determine how much entropy does your system have prior making a request for random data (**Passphrase** does this when runs as a script). You should always have more than 128 bits or the call to `os.urandom()` might hang or fail.
+
+### Requirements
 
 * **Python 3.5+**.
 * [Flake8](http://flake8.pycqa.org/en/latest/) [optional] for linting.

Makefile

@@ -10,7 +10,7 @@ TMPDIR := $(shell mktemp -d --tmpdir "passphrase.XXXXXXXXXX")
 all:
 	@echo "Passphrase by HacKan (https://hackan.net)"
 	@echo "Commands for this makefile:"
-	@echo -e "\tinstall\n\taltinstall\n\tuninstall\n\taltuninstall\n\tpackage-install\n\tpackage-uninstall\n\tlint\n\ttest\n\tcoverage\n\ttimeit\n\tclean"
+	@echo -e "\tinstall\n\taltinstall\n\tuninstall\n\taltuninstall\n\tpackage-install\n\tpackage-uninstall\n\tdevenvironment\n\tlint\n\ttest\n\tcoverage\n\ttimeit\n\tclean"
 
 clean:
 	@rm -vrf \
@@ -85,4 +85,16 @@ coverage:
 timeit:
 	python3 -m timeit -n 100 -r 10 -s 'import os' 'os.system("python3 -m passphrase -w6 -m")'
 
-.PHONY: install altinstall uninstall altuninstall lint test coverage timeit clean
+devenvironment:
+	@echo "Creating virtualenv"
+	@[ -d venv ] || virtualenv -p python3 venv
+	@echo "Installing dev dependencies"
+	venv/bin/pip install -r requirements-dev.txt
+	@echo "Installing passphrase"
+	@venv/bin/python3 setup.py --fullname
+	@venv/bin/python3 setup.py --description
+	@venv/bin/python3 setup.py --url
+	venv/bin/python3 setup.py install
+	@echo -e '\nAll done. You might want to activate the virtualenv (I can not do it for you): `source venv/bin/activate`'
+
+.PHONY: install altinstall uninstall altuninstall lint test coverage timeit clean devenvironment