README.md: remove duplication of CONTRIBUTING.md content
README.md: remove duplication of CONTRIBUTING.md content

artspb/intellij-sdk-docs,JetBrains/intellij-sdk-docs,artspb/intellij-sdk-docs,JetBrains/intellij-sdk-docs,JetBrains/intellij-sdk-docs,artspb/intellij-sdk-docs,artspb/intellij-sdk-docs