docs: reorganize docs pages and CONTRIBUTING.md (#1705)

docs/accounts-authentication.md

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+# Accounts authentication
+
+## GitHub
+
+The GitHub authentication has been patched to use personal access token.
+
+Here how to create a new personal access token: https://docs.github.com/en/authentication/keeping-your-account-and-data-secure/creating-a-personal-access-token
+
+## Microsoft
+
+The Microsoft authentication hasn't been patched so its status is unknown.
+
+## When does it happened?
+
+An account authentication occurs only when an extension is asking for it.
+
+For `GitLens`, since the `12 non-plus` version, it won't ask for any new authentication.