Update README installation instructions (#172)

* Update README.md with development install

---------

Co-authored-by: Tommy Odland <tommy.odland>

README.md

@@ -26,22 +26,20 @@ This algorithm is particularly effective for problems with a large number of par
 pip install iterative_ensemble_smoother
 ```
 
-## Usage
-
-**iterative_ensemble_smoother** mainly implements `SIES` and `ESMDA` classes. Check out
-the examples section to see how to use them.
-
-
-## Building from source
-
-To build **iterative_ensemble_smoother** from source:
+If you want to do development, then run:
 
-```bash
+```text
 git clone https://github.com/equinor/iterative_ensemble_smoother.git
 cd iterative_ensemble_smoother
-pip install .
+<create environment>
+pip install --editable '.[doc,dev]'
 ```
 
+## Usage
+
+**iterative_ensemble_smoother** mainly implements the two classes `SIES` and `ESMDA`.
+Check out the examples section to see how to use them.
+
 ## Building the documentation
 
 ```bash