Add related projects to readme

[amarvin]

• https://github.com/SAP/PyRFC
• installing SAP NW SDK: https://github.com/mikewolfli/sapnwrfcsdk
• Demos using pyrfc
  • https://community.sap.com/t5/technology-blogs-by-members/connecting-python-with-sap-step-by-step-guide/ba-p/13452893
• Packages that use pyrfc
  • https://github.com/victorouttes/sap-rfc-data-collector
  • https://github.com/redbearder/sapspa
  • https://github.com/jduncan8142/saprfc
  • https://github.com/CLFPosthumus/SAP_PyRFC
  • https://github.com/DataZooDE/erpl
• Packages that control SAP GUI Logon
  • https://github.com/alekczapski/sap_python (although has info about using pyrfc with version of SAP NW SDK included in SAP GUI Logon)
• https://github.com/victorouttes/sap-rfc-data-management