docs: note about existing content at same path on different branches

vintro

2023-08-14 f1c9ca495e450ecb62dade70c4b60d86e106f79c

 quartz/processors/emit.ts

@@ -37,7 +37,6 @@
      }
    } catch (err) {
      trace(`Failed to emit from plugin \`${emitter.name}\``, err as Error)
      throw err
    }
  }