docs: update WAM doc about elevated users

Since GCM 2.1, we are using a newer version of MSAL that uses the new
MSAL runtime that solves the COM security issues that presented with
elevated processes.

Update our documentation to recommend people update to fix this problem.

Author: mjcheetham

docs/windows-broker.md

@@ -154,6 +154,14 @@ As far as we can tell, there are no workarounds for either of these behaviors
 
 ## Running as administrator
 
+### GCM 2.1 and later
+
+From version 2.1 onwards, GCM uses a version of the [Microsoft Authentication
+Library (MSAL)][msal-dotnet] that supports use of the Windows
+broker from an elevated process.
+
+### Previous versions
+
 The Windows broker ("WAM") makes heavy use of [COM][ms-com], a remote procedure
 call (RPC) technology built into Windows. In order to integrate with WAM, Git
 Credential Manager and the underlying
@@ -181,8 +189,10 @@ See https://aka.ms/gcm/wamadmin for more information.
 
 In order to fix the problem, there are a few options:
 
-1. Run Git or Git Credential Manager from non-elevated processes.
-2. Disable the broker by setting the
+1. Update to the [latest Git for Windows][git-for-windows-latest]
+   **(recommended)**.
+2. Run Git or Git Credential Manager from non-elevated processes.
+3. Disable the broker by setting the
    [`GCM_MSAUTH_USEBROKER`][GCM_MSAUTH_USEBROKER]
    environment variable or the
    [`credential.msauthUseBroker`][credential.msauthUseBroker]
@@ -206,3 +216,4 @@ In order to fix the problem, there are a few options:
 [ms-com]: https://docs.microsoft.com/en-us/windows/win32/com/the-component-object-model
 [msal-dotnet]: https://aka.ms/msal-net
 [devbox]: https://azure.microsoft.com/en-us/products/dev-box
+[git-for-windows-latest]: https://git-scm.com/download/win