Add /preservetimestamp option

What's Changed

• docs(README): Update with dotnet tool installation instructions by @fourpastmidnight in #377
• Add /preservetimestamp command line option by @myhomeiot in #381

New Contributors

• @fourpastmidnight made their first contribution in #377
• @myhomeiot made their first contribution in #381

Full Changelog: 2.0.35...2.0.36

• https://www.nuget.org/packages/ILRepack/2.0.36
• https://www.nuget.org/packages/ILRepack.Lib/2.0.36
• https://www.nuget.org/packages/dotnet-ilrepack/1.0.2