Update Cygwin-Build-for-Windows.md

I had a hard time to figure everything out, so I thought it could be posted here.
Probably I forgot one or the other step, but the majority should be covered.
Some reformatting might be needed.
Best regards,
Andreas

Author: chiefenne

_docs/Cygwin-Build-for-Windows.md

@@ -24,3 +24,64 @@ At the package selection step, search for the following terms and select the ass
 * python: install the packages under the python sub-heading
 * cpp: all debug, pre-processor, regular expression packages. 
 
+#### Example SU2 installation on WINDOWS 10 using 64-bit Cygwin
+The shell used for all command line steps is the the default Cygwin bash shell.
+                                                                                               
+1) Install CYGWIN (64-bit version)                                                             
+   a) Download and run https://www.cygwin.com/setup-x86_64.exe                                 
+   b) Install development tools (also 64-bit versions):                                        
+     i) gcc, gfortran, python3.7, openmpi, automake, libtools, autoconf, etc.                  
+     ii) python-configobj needs to be installed for the same python version                    
+         (Python module for handling config files)                                             
+         often there are installation problems (not yet figured out when and why)              
+         after installation it should reside in the folder /usr/bin as shown below                
+     iii) folder /usr/bin as it should be for python3.7 and python-config                      
+         lrwxrwxrwx 1 Andreas None   14 17. Mrz 19:29 /usr/bin/python3.7 -> python3.7m.exe     
+         -rwxr-xr-x 1 Andreas None 3,3K 17. Mrz 19:46 /usr/bin/python3.7-config                
+         -rwxr-xr-x 1 Andreas None 9,1K 15. Feb 10:05 /usr/bin/python3.7m.exe                  
+         -rwxr-xr-x 1 Andreas None 3,3K 17. Mrz 19:46 /usr/bin/python3.7m-config
+
+2) Set Python version for the installation process                                                       
+   export PYTHON=/usr/bin/python3.7                                                                      
+                                                                                                         
+3) Goto folder where the SU2 source distribtution has been unzipped                                      
+   a) download the SU2 source installation file for version 6.2.0                                                               
+      https://github.com/su2code/SU2/archive/v6.2.0.tar.gz                                               
+   b) unzip and untar                                                                                    
+   c) change into the folder where files were untarred                                                    
+      NOTE: this is later (see step 7) the folder where the SU2_HOME variable points to                  
+                                                                                                         
+4) Launch following configure command:                                                                   
+   NOTE: didn't get tecio working, therefore disabled with --disable-tecio                               
+   NOTE: "--enable-mpi-cxx" instead of "--enable-mpi"                                                    
+   (see http://cygwin.1069669.n5.nabble.com/libmpi-cxx-dll-a-missing-td142324.html)                      
+                                                                                                         
+  ./configure --prefix=path_where_you_want_the_Executables --disable-tecio --enable-mpi-cxx CXXFLAGS=-O3 
+                                                                                                         
+5) Compile and link using:                                                                               
+   make                                                                                                  
+                                                                                                         
+6) Not really needed (if a setup like in 7 is used)                                                      
+   make install                                                                                          
+                                                                                                         
+7) Add the $SU2_HOME and $SU2_RUN environment variables to ~/.bashrc (and "source ~/.bashrc")
+                                                                                                                 
+   export SU2_RUN="path_where_you_want_the_Executables" (use same folder here as in the configure command above) 
+   export SU2_HOME="/d/software/CFD/SU2/SU2-6.2.0"  <-- UPDATE THIS folder to your environment                   
+   export PATH=$PATH:$SU2_RUN                                                                                    
+   export PYTHONPATH=$PYTHONPATH:$SU2_RUN                                                                        
+                                                                                                                 
+8) cd to the QuickStart folder and try serial and parallel versions                                              
+                                                                                                                 
+   SERIAL command:                                                                                               
+                                                                                                                 
+   SU2_CFD.exe inv_NACA0012.cfg                                                                                  
+                                                                                                                 
+   PARALLEL command:                                                                                             
+   (mpirun and mpiexec should be the same; mpiexec recommended as standard command)                              
+   (-oversubscribe allows more processes than cores)                                                             
+   (although I have 8 cores, even with "-n 6" I had to use the option)                                           
+   (otherwise I got: There are not enough slots available in the system ...)                                     
+                                                                                                                 
+   mpiexec -n 6 -oversubscribe SU2_CFD.exe inv_NACA0012.cfg
+