error tool doc (#490)

* error tool doc

* fix wenqu comments

* fix wenqu comments2

tools/ob_error/README.md

 # What is ob_error
 
-ob_error is the error tool of OceanBase.
-
-An error tool can return the information, reason and solution corresponding to the error code which entered by the user.
-
-It saves the trouble of looking up documents.
+ob_error is an error tool for OceanBase Database. ob_error returns information, cause, and possible solutions for the error code you enter. With the help of ob_error, it is not necessary to look up the documents for basic error information.
 
 ## How to build
 
-### debug mode
+### Debug mode
 
-```shell
+```bash
 bash build.sh debug --init
 cd build_debug
 make ob_error
 cp tools/ob_error/src/ob_error /usr/local/bin
 ```
 
-`ob_error` will generated in `DEBUG_BUILD_DIR/tools/ob_error/src/ob_error` by default.
+The compiled product for `ob_error` is stored in `DEBUG_BUILD_DIR/tools/ob_error/src/ob_error` by default.
 
-### release mode
+### Release mode
 
-```shell
+```bash
 bash build.sh release --init
 cd build_release
 make ob_error
 cp tools/ob_error/src/ob_error /usr/local/bin
 ```
 
-`ob_error` will generated in `RELEASE_BUILD_DIR/tools/ob_error/src/ob_error` by default.
+The compiled product for `ob_error` is stored in `RELEASE_BUILD_DIR/tools/ob_error/src/ob_error` by default.
 
-### RPM packges
+### RPM packages
 
-NOTE: this is not support now.
+`ob_error` is provided in `oceanbase-ce-utils-3.1.1-4.el7.x86_64.rpm`. If you only need `ob_error`, use the `rpm2cpio` command to get `ob_error`.
 
-```shell
-bash build.sh rpm --init && cd build_rpm && make -j16 rpm
-rpm2cpio oceanbase-ce-3.1.0-1.alios7.x86_64.rpm | cpio -idmv ./home/admin/oceanbase/bin/ob_error
+```bash
+rpm2cpio oceanbase-ce-utils-3.1.1-4.el7.x86_64.rpm | cpio -idmv ./home/admin/oceanbase/bin/ob_error
 cp home/admin/oceanbase/bin/ob_error /usr/local/bin
 ```
 
-`ob_error` will included in `oceanbase-ce-3.1.0-1.alios7.x86_64.rpm`.
-Because you just need `ob_error`, you can use `rpm2cpio` to do it.
-
 ## How to use
 
-You can search error message by only enter the error code.
-
-Then you will get the error message corresponding to OS, Oracle and MySQL modes, and OceanBase own error (if any exists).
+You can search for error messages by only entering the error code. Then you will get the error message corresponding to the operation system, Oracle mode, MySQL mode, and OceanBase error (if any). For example:
 
-such as:
-
-```shell
+```bash
 $ob_error 4001
 
 OceanBase:
@@ -67,13 +55,11 @@ Oracle:
         OB_ERR_SEQ_OPTION_MUST_BE_INTEGER(-4317)
 ```
 
-Also, you can search error message of specific mode by adding a prefix (we called facility).
-
-When the facility is `my`, if the error code is not an error which exists in MySQL, you will get the OceanBase error info(if it exists). Otherwise, you will get the error info of MySQL mode.
+Also, you can search error messages for a specific mode by adding a prefix (also known as a facility).
 
-such as:
+When the facility is `my`, if the error code is not an error in MySQL, you will get the OceanBase error info(if any). Otherwise, you will get the error info of MySQL mode.
 
-```shell
+```bash
 $ob_error my 4000
 
 OceanBase:
@@ -95,10 +81,9 @@ MySQL:
         INCORRECT_ARGUMENTS_TO_ESCAPE(-5832)
 ```
 
-When the facility is `ora` or `pls`, you will get the error info of Oracle mode(if it exists).
-such as:
+When the facility is `ora` or `pls`, you will get the error info of Oracle mode(if any). For example:
 
-```shell
+```bash
 $ob_error ora 51
 
 Oracle:
@@ -108,11 +93,9 @@ Oracle:
         OB_ERR_TIMEOUT_ON_RESOURCE(-5848)
 ```
 
-Further more, there is an exceptional case. If you use the `-a` option, you will get the OceanBase own error info and the error info of Oracle mode (if any exists).
-
-such as:
+Furthermore, there is an exceptional case. If you use the `-a` option, you will get OceanBase error info and Oracle mode error info (if any). For example:
 
-```shell
+```bash
 $ob_error ora 600 -a 5727
 
 OceanBase:
@@ -128,39 +111,39 @@ Oracle:
         OB_ERR_PROXY_REROUTE(-5727)
 ```
 
-Note: `-a` option is designed to find `ORA-00600` error which has an `arguments` (those Oracle internal error).
+> **NOTE**: `-a` option helps to find `ORA-00600` error which has `arguments` (those Oracle internal errors).
 
-You can find more test example in [expect_result](test/expect_result.result).
+You can find more test examples in [expect_result](test/expect_result.result).
 
-Further more, you can get the complete user manual by `--help` option.
+Furthermore, you can get the complete user manual by `--help` option.
 
-```shell
+```bash
 ob_error --help
 ```
 
 ## How to add error cause/solution
 
-*This part is for developers.*
+> **NOTE**: This section is for developers.
 
 For example:
 
-The ob error `4000` in `src/oberror_errno.def` defined as
+The ob error `4000` in `src/oberror_errno.def` is defined as:
 
-```shell
+```bash
 DEFINE_ERROR(OB_ERROR, -4000, -1, "HY000", "Common error");
 ```
 
-If you want to add the cause and solution info, you can change the define as
+If you want to add the cause and solution info, you can change the definition as:
 
-```shell
+```bash
 DEFINE_ERROR(OB_ERROR, -4000, -1, "HY000", "Common error", "CAUSE", "SOLUTION");
 ```
 
-And then regenerate the `src/lib/ob_errno.h`、`src/share/ob_errno.h` and `src/share/ob_errno.cpp` by
+And then regenerate the `src/lib/ob_errno.h`、`src/share/ob_errno.h` and `src/share/ob_errno.cpp` by using these commands:
 
-```shell
+```bash
 cd src/share
 ./gen_errno.pl
 ```
 
-Finally back to `BUILD_DIR` to remake `ob_error`.
+Then you go to `BUILD_DIR` to remake `ob_error`.