Reduced the redundancy on requirements.txt, and highlighted the devel…

…opment installation mode with pip. (#334)

MANIFEST.in

@@ -1,5 +1,6 @@
 include README.md
 include LICENSE
+include requirements.txt
 graft opsdroid
 include opsdroid/configuration/example_configuration.yaml
 recursive-exclude * *.py[co]

docs/contributing.md

@@ -19,8 +19,8 @@ All contributors to the project, including [jacobtomlinson](https://github.com/j
 git clone https://github.com/opsdroid/opsdroid.git
 cd opsdroid
 
-# install project dependencies
-pip install -r requirements.txt
+# install the project in "editable" mode
+pip install -e .
 
 # run opsdroid
 python -m opsdroid

setup.py

@@ -9,12 +9,13 @@
 PACKAGES = find_packages(exclude=['tests', 'tests.*', 'modules',
                                   'modules.*', 'docs', 'docs.*'])
 
-REQUIRES = [
-    'arrow==0.10.0',
-    'aiohttp==2.1.0',
-    'pycron==0.40',
-    'pyyaml==3.12'
-]
+
+# For now we simply define the install_requires based on the contents
+# of requirements.txt. In the future, install_requires may become much
+# looser than the (automatically) resolved requirements.txt.
+with open(os.path.join(HERE, 'requirements.txt'), 'r') as fh:
+    REQUIRES = [line.strip() for line in fh]
+
 
 setup(
     name=PACKAGE_NAME,