Update cli-ref-environment-variables.md

Author: karann-msft

docs/tools/cli-ref-environment-variables.md

@@ -29,3 +29,4 @@ In general, options specified directly on the command line or in NuGet configura
 | NUGET_RESTORE_MSBUILD_VERBOSITY | Sets the MSBuild log verbosity. | Default is *quiet* ("/v:q"). Possible values *q[uiet]*, *m[inimal]*, *n[ormal]*, *d[etailed]*, and *diag[nostic]*. |
 | NUGET_SHOW_STACK | Determines whether the full exception (including stack trace) should be displayed to the user. | Specified as *true* or *false* (default). |
 | NUGET_XMLDOC_MODE | Determines how assemblies XML documentation file extraction should be handled. | Supported modes are *skip* (do not extract XML documentation files), *compress* (store XML doc files as a zip archive) or *none* (default, treat XML doc files as regular files). |
+| NUGET_CERT_REVOCATION_MODE | Determines how the revocation status check of the certificate used to sign a package, is pefromed when a signed package is installed or restored. When not set, defaults to `online`.| Possible values *online* (default), *offline*.  Related to [NU3028](../reference/errors-and-warnings/NU3028.md) |