doc: Add install instructions to README.md

Author: johan-bjareholt

README.md

@@ -1,18 +1,29 @@
 aw-core
 =======
 
-[![Build Status Travis](https://travis-ci.org/ActivityWatch/aw-core.svg?branch=master)](https://travis-ci.org/ActivityWatch/aw-core) 
+[![Build Status Travis](https://travis-ci.org/ActivityWatch/aw-core.svg?branch=master)](https://travis-ci.org/ActivityWatch/aw-core)
 [![Build Status Appveyor](https://ci.appveyor.com/api/projects/status/h5cvxoghh1wr4ycr/branch/master?svg=true)](https://ci.appveyor.com/project/ErikBjare/aw-core/branch/master)
 [![codecov](https://codecov.io/gh/ActivityWatch/aw-core/branch/master/graph/badge.svg)](https://codecov.io/gh/ActivityWatch/aw-core)
 
 
 Core library for ActivityWatch.
 
 
-Contents
-========
+## Contents
 
  - Models
  - Schemas
  - Filtering algorithms for sensitive data
 
+
+## How to install
+
+To install the latest git version directly from github without cloning, run
+`pip install git+https://github.com/ActivityWatch/aw-core.git`
+
+To install from a cloned version, cd into the directory and run
+`poetry install` to install inside an virtualenv. If you want to install it
+system-wide it can be installed with `pip install .`, but that has the issue
+that it might not get the exact version of the dependencies due to not reading
+the poetry.lock file.
+