You could have claude --init create this hook and then it gets into the context at start and resume

Or create it in some other way

    {
      "hookSpecificOutput": {
        "hookEventName": "SessionStart",
        "additionalContext": "<contents of your file here>"
      }
    }

I thought it was such a good suggestion that I made this just now and made it global to inject README at startup / resume / post compact - I'll see how it works out

    #!/bin/bash
    # ~/.claude/hooks/inject-readme.sh

    README="$(pwd)/README.md"

    if [ -f "$README" ]; then
      CONTENT=$(jq -Rs . < "$README")
      echo "{\"hookSpecificOutput\" :{\"hookEventName\":\"SessionStart\",\"additionalContext\":${CONTENT}}}"
      exit 0
    else
      echo "README.md not found" >&2
      exit 1
    fi

with this hook

    {
      "hooks": {
        "SessionStart": [
          {
            "matcher": "startup|clear|compact",
            "hooks": [
              {
                "type": "command",
                "command": "~/.claude/hooks/inject-readme.sh"
              }
            ]
          }
        ]
      }
    }