add instructions of pip install in editable mode

Author: ShuhuaGao

docs/src/juliacall.md

@@ -9,8 +9,24 @@ For now, you can pip install this package directly from github as follows:
 pip install git+https://github.com/cjdoris/PythonCall.jl
 ```
 
+### Installation in editable mode
+
 Developers may wish to clone the repo directly and pip install the module in editable mode.
-This guarantees you are using the latest version of PythonCall in conjunction with juliacall.
+This guarantees you are using the latest version of PythonCall in conjunction with juliacall. Please proceed with either option below.
+
+1. Intall directly from GitHub. You may want to change the branch after `@` to the one you like.
+
+    ```bash
+    pip install -e git+https://github.com/cjdoris/PythonCall.jl@master#egg=juliacall
+    ```
+
+    The source code will be downloaded into a *src* subfolder of the current directory.
+
+2. Alternatively, first clone this repository and then install from the local source. Please replace the directory below with your actual one.
+
+    ```bash
+    pip install --user -e git+file:///home/shuhua/github/PythonCall.jl@master#egg=juliacall 
+    ```
 
 Note also that regardless of installing `juliacall`, a module called `juliacall` will
 always be loaded into the interpreter by `PythonCall`. This means that other Python