docs(install): fix link to the ".NET tool" section (#1007)

Something I noticed today, while looking for a way to install Git
Credential Manager for Windows/ARM64.

Author: ldennington

docs/install.md

@@ -64,7 +64,7 @@ sudo /usr/local/share/gcm-core/uninstall.sh
 
 ### .NET tool :star:
 
-See the [.NET tool](#.NET-tool) section below for instructions on this
+See the [.NET tool](#net-tool) section below for instructions on this
 installation method.
 
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