Add documentation for update-milestone automation

[tarunvijwani]

This PR adds the documentation for the update-milestone automation.

Changes in the PR

• Add the README.MD file for the update-milestone automation.

Testing

1. Navigate to the documentation page.
2. Confirm the content mentioned in the document is correct.

[github-actions[bot]]

:loop: Code coverage

Filename	Statements	Branches	Functions	Lines
lib/automations/todos/utils/get-todos.js	100%	100%	100%	100%
lib/automations/todos/utils/get-diff.js	100%	100%	100%	100%
lib/automations/todos/utils/parse-to-do.js	100%	97.67%	100%	100%
lib/automations/todos/utils/get-details.js	100%	90.91%	100%	100%
lib/debug.js	66.67%	50%	100%	66.67%
lib/automations/todos/utils/check-for-duplicate-issue.js	100%	100%	100%	100%
lib/automations/todos/index.js	100%	100%	100%	100%
lib/automations/todos/runner.js	88.89%	66.67%	100%	88.89%
lib/automations/todos/pull-request-handler.js	90.48%	83.33%	100%	90.48%
lib/automations/todos/templates/index.js	100%	100%	100%	100%
lib/automations/todos/templates/comment.js	100%	100%	100%	100%
lib/automations/todos/templates/issue.js	100%	100%	100%	100%
lib/automations/todos/templates/issue-from-merge.js	100%	100%	100%	100%
lib/automations/todos/templates/title-change.js	100%	100%	100%	100%
lib/automations/todos/templates/reopen-closed.js	100%	100%	100%	100%
lib/utils/index.js	100%	100%	100%	100%
lib/utils/milestones.js	96.3%	90%	100%	96.3%
lib/utils/helpers.js	85.71%	66.67%	100%	83.33%
lib/automations/todos/pull-request-merge-handler.js	91.3%	87.5%	100%	91.3%
lib/automations/todos/utils/reopen-closed.js	100%	100%	100%	100%
lib/automations/todos/push-handler.js	92%	90%	100%	92%
lib/automations/todos/issue-rename-handler.js	100%	100%	100%	100%
lib/automations/assign-milestone/index.js	100%	100%	100%	100%
lib/automations/assign-milestone/runner.js	86.67%	50%	100%	86.67%
lib/automations/assign-milestone/pull-request-review-handler.js	85.71%	63.64%	100%	85.71%
lib/automations/assign-milestone/get-version.js	76.92%	80%	100%	76.92%
lib/automations/assign-milestone/get-config.js	30.77%	0%	0%	30.77%
lib/automations/release/config/validate-config.js	92.59%	95%	100%	92.59%
lib/automations/release/index.js	100%	100%	100%	100%
lib/automations/release/runner.js	88.24%	66.67%	100%	88.24%
lib/automations/release/branch-create-handler.js	82.43%	68.42%	75%	83.56%
lib/automations/release/templates/index.js	83.33%	46.67%	75%	83.33%
lib/automations/release/utils/index.js	100%	100%	100%	100%
lib/automations/release/utils/get-release-version.js	90.91%	87.5%	100%	90.91%
lib/automations/release/utils/is-patch-release.js	100%	100%	100%	100%
lib/automations/release/utils/get-release-branch.js	62.5%	55.56%	100%	62.5%
lib/automations/release/utils/duplicate-pr-checker.js	100%	100%	100%	100%
lib/automations/release/utils/has-milestone.js	100%	100%	100%	100%
lib/utils/changelog/index.js	100%	100%	100%	100%
lib/utils/changelog/common/changelog.js	83.96%	56.1%	86.49%	83%
lib/automations/release/attach-changelog-new-release-handler.js	92.86%	75%	100%	92.86%
lib/automations/release/config/index.js	75%	0%	100%	75%
lib/index.js	0%	0%	0%	0%
lib/automations.js	0%	100%	100%	0%
lib/typedefs.js	0%	100%	100%	0%
lib/automations/update-milestone/index.js	0%	100%	100%	0%
lib/automations/update-milestone/runner.js	0%	0%	0%	0%
lib/automations/update-milestone/update-milestone-handler.js	0%	0%	0%	0%
lib/automations/update-milestone/get-config.js	0%	0%	0%	0%
lib/utils/version.js	0%	0%	0%	0%
lib/if-not-fork.js	0%	0%	0%	0%