[NO JIRA] Rename file to avoid overriding root README.md

.github/README.txt → .github/important.txt

@@ -1,3 +1,6 @@
 The empty PULL_REQUEST_TEMPLATE.md file is here to override the one defined in /docs/PULL_REQUEST_TEMPLATE.md.
 
 This allows us to not show a template for PRs on the sonarsource/sonar-enterprise repository, while leaving a template for the public sonarsource/sonarqube repository.
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+Note: do not call this file "README", as it would override the one in the repository root.
+