Add an Installation page and rework the Download page

[vy]

[Disclaimer: I am not a .NET developer. Apologies in advance if I say something nonsense.]

Currently, in the Log4Net website, I am not able to quickly answer the following questions:

• Is Log4Net available in NuGet? If so, what are its package coordinates?
• How can I quickly write a .NET application using Log4Net NuGet packages?

I suggest to update the current website as follows:

• Create an Installation page addressing the above questions to quickly get users started
• Create a Download page (currently the Download link in the left menu points to the Logging Services Download page), similar to the one Log4j has, containing two bullets:
  • "Do you want to install Log4Net in your .NET application? See the Installation page."
  • "Do you want to manually download the artifacts? See the Logging Services download page."