title: How to update a config file section using git config?
body: <p>I need to add <code>branch = super_foo</code> to the existing <code>superproject</code> section in test_config file:</p>
  
  <pre><code>$ cat .test_config
  [superproject "mysuper"]
      url = https://server.com/test/mysuper
  
  [submodule "tsn-inc"]
      url = url = https://server.com/test/foo_s
      branch = foo
  </code></pre>
  
  <p>This works:</p>
  
  <pre><code>git config -f .test_config --add superproject.mysuper.branch super_foo
  </code></pre>
  
  <p>But, "mysuper" is not a known value, so I tried below as there will be only one superproject section.</p>
  
  <pre><code>git config -f .test_config --add superproject.*.branch super_foo
  </code></pre>
  
  <p>it added a new section as below:</p>
  
  <pre><code>[superproject "*"]
      branch = super_foo
  </code></pre>
  
  <p>Instead, I want to add branch to the existing superproject section, is there a way to do this?</p>