Translate readme.txt in chinese

doc/readme-zh.md

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+```
+       ╭╮
+╭─┬┬┬──┤└╮
+╰┴┴─┴┴┴┴─╯
+```
+***
+麻木的拇指是处理生活中常见的数字运算，单位计算与日期计算的工具
+***
+#### 举例如下
+```
+
+    $ numb
+    Enter `q` to quit
+    > 3735928559 >> 16 in hex
+      0xdead
+    > 1920/1080 in rat
+      16/9
+    > sin(pi/3)
+      0.87
+    > 3 millilightsecond to mile
+      558.85 mile
+    > 10 mile/hour to metre/sec
+      4.47 metre/sec
+    > total_grains = 2^64 - 1
+      18446744073709551615
+    > 3 GB / (15 Mbps) to minute
+      26.67 minute
+    > time in London
+      13:04
+    > today + 10 days
+      05 Jun 2022
+    > today - {1999-09-09} to months
+      272.54 month
+```
+#### 安装
+```
+# build with Go >= 1.16
+$ go install github.com/nkanaev/numb@latest
+```
+#### 更多帮助
+```
+   doc/help.txt     手册, 示例
+    doc/spec.txt     命令行语法
+    doc/dump.txt     各种设计笔记
+    doc/todo.txt     待办事项
+```
+
+
+