Words in README for mu4e layer

[davidpiano]

Installation instructions are contradictory:

• Install
  In order to use this layer you must install =mu= and =mu4e= separately.
  Typically =mu4e= will be bundled with =mu= (this is the case on many Linux
  distributions).

Something like the following might be better:

• Install
  In order to use this layer you must install two applications on your system, =mu= and =mu4e=.
  On many Linux distributions they are bundled together, but make sure you have both before proceeding.

[smile13241324]

Sounds good, would you mind opening a PR for it?

[davidpiano]

I'm willing, but have never opened a PR before, or made any contribution to anything. I'll go and try it - I assume it's not difficult.

[smile13241324]

Yeah its really pretty easy just do your work in your fork based on develop, then propose the PR you can do this via githubs web ui and I will have a look.