feat:用户管理邮箱长度提示

src/views/admin/sys-user/index.vue

@@ -208,7 +208,7 @@
             </el-col>
             <el-col :span="12">
               <el-form-item label="邮箱" prop="email">
-                <el-input v-model="form.email" placeholder="请输入邮箱" maxlength="50" />
+                <el-input v-model="form.email" placeholder="请输入50字符内的邮箱" maxlength="50" />
               </el-form-item>
             </el-col>
           </el-row>