Add a guide about applying licenses

[Stephen-Gates]

Draft guide. Feedback welcome

Please check both content and markdown

I had trouble following the readme instructions to run lektor - I got

Stephen-MacBook-Pro:website Stephen$ lektor server
 * Project path: /Users/Stephen/Documents/GitHub/website/frictionlessdata.lektorproject
 * Output path: /Users/Stephen/Library/Caches/Lektor/builds/7f331e67c9cf1ced414aa35c8e51207c
 * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)
Started source info update
Finished source info update in 0.01 sec
Traceback (most recent call last):
  File "/Applications/Lektor.app/Contents/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/lektor/devserver.py", line 44, in build
    builder.update_all_source_infos()
  File "/Applications/Lektor.app/Contents/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/lektor/builder.py", line 1129, in update_all_source_infos
    self.update_source_info(prog, build_state)
  File "/Applications/Lektor.app/Contents/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/lektor/builder.py", line 1047, in update_source_info
    build_state.write_source_info(info)
  File "/Applications/Lektor.app/Contents/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/lektor/builder.py", line 240, in write_source_info
    ''', [info.path, info.alt, lang, info.type, source, title])
OperationalError: attempt to write a readonly database
U index.html
U index.html
----------------------------------------
Exception happened during processing of request from ('127.0.0.1', 64589)

[Stephen-Gates]

Got Lektor working (sudo lector server). Markdown all good.

Content review requested

Fixes #157