Install guide section href fixup

[Rainyan]

• Update the install guide page section anchor href
  • from: https://neotokyorebuild.github.io/guide/install/#installing-ntre (old section title)
  • to: https://neotokyorebuild.github.io/guide/install/#2%2E-installing-ntre (new section title)
• Add troubleshooting section for missing Steam library entry

[AdamTadeusz]

would it be within the scope of this pr to update the link to the decompile to maybe your fork of it? In contributing.md

[Rainyan]

would it be within the scope of this pr to update the link to the decompile to maybe your fork of it? In contributing.md

Do you mean the file https://github.com/NeotokyoRebuild/neo/blob/master/CONTRIBUTING.md ? That's a different repo so would probably have to be a separate PR