Update how-to-build.rst

Documentation/how-to-build.rst

@@ -73,13 +73,18 @@ Dependencies
 
 * One of three CRC packages are required. Pick one:
 
+  - for all OS's
+  
     .. code-block:: shell-session
+        
         pip3 install --user crc16
             
     .. code-block:: shell-session
+        
         pip3 install --user crcmod
             
     .. code-block:: shell-session
+        
         pip3 install --user crcmod
         
 * **python3-pillow**: Python Image Library