Update install_and_test.md

install_and_test.md

@@ -22,7 +22,9 @@ To run the C and python tests of the installed `hotwheels` components, run:
 python -m hotwheels.checkup hotwheels
 ```
 
-# Install custom versions
+# Install developer way
+
+## Install custom versions
 
 In case you want to run the module with other `hotwheel` component version you can install each manually:
 
@@ -33,7 +35,7 @@ pip install git+ssh://git@git.ia2.inaf.it/hotwheels/timestep.git@v0.0.0alpha
 pip install git+ssh://git@git.ia2.inaf.it/hotwheels/PM.git@v0.0.0alpha
 ```
 
-# If you need to put hands on the source code
+## If you need to put hands on the source code
 
 In case you find that you need to edit the source code of hotwheels (maybe you found a bug), you
 can re-install a python module in **editable mode (use -e in pip install)**. For instance, let's suppose that now you need to edit the timestep module and re-run all tests. You can do the following 
@@ -49,7 +51,7 @@ pip install -e .
 #
 ```
 
-# Bulk install of all modules
+## Bulk install of all modules
 
 In case you need to work on many modules, you can clone and install all default packages with the [cloneall.bash](cloneall.bash) script:
 
@@ -66,7 +68,7 @@ You can insert a personalised number of repos by running for instance `cloneall.
 
 
 
-# Environment variables
+## Environment variables
 
 Here below some relevant environment variables to change hotwheels default settings: