Update INSTALL.md (#1283)

* Update INSTALL.md

Signed-off-by: sahuang <xiaohaix@student.unimelb.edu.au>

* Update INSTALL.md

Signed-off-by: sahuang <xiaohaix@student.unimelb.edu.au>

* Update INSTALL.md

update shell script

Signed-off-by: sahuang <xiaohaix@student.unimelb.edu.au>

* Update INSTALL.md

Signed-off-by: sahuang <xiaohaix@student.unimelb.edu.au>

INSTALL.md

@@ -23,10 +23,11 @@
 
 ### Requirements
 
-- Ubuntu 18.04 or higher
-- CentOS 7
+- Operating system
+  - Ubuntu 18.04 or higher
+  - CentOS 7
 
-If your operating system does not meet the requirements, we recommend that you pull a Docker image of [Ubuntu 18.04](https://docs.docker.com/install/linux/docker-ce/ubuntu/) or [CentOS 7](https://docs.docker.com/install/linux/docker-ce/centos/) as your compilation environment.
+  If your operating system does not meet the requirements, we recommend that you pull a Docker image of [Ubuntu 18.04](https://docs.docker.com/install/linux/docker-ce/ubuntu/) or [CentOS 7](https://docs.docker.com/install/linux/docker-ce/centos/) as your compilation environment.
   
 - GCC 7.0 or higher to support C++ 17
 - CMake 3.12 or higher
@@ -40,14 +41,21 @@ For GPU-enabled version, you will also need:
 
 #### Step 1 Install dependencies
 
+##### Install in Ubuntu
+
 ```shell
 $ cd [Milvus root path]/core
 $ ./ubuntu_build_deps.sh
 ```
 
-#### Step 2 Build
+##### Install in CentOS
 
-##### Build in Ubuntu
+```shell
+$ cd [Milvus root path]/core
+$ ./centos7_build_deps.sh
+```
+
+#### Step 2 Build
 
 ```shell
 $ cd [Milvus root path]/core
@@ -60,13 +68,6 @@ or
 $ ./build.sh -t Release
 ```
 
-##### Build in CentOS
-
-```shell
-$ cd [Milvus root path]/core
-$ ./centos7_build_deps.sh
-```
-
 By default, it will build CPU-only version. To build GPU version, add `-g` option.
 
 ```shell
@@ -79,7 +80,7 @@ If you want to know the complete build options, run the following command.
 $./build.sh -h
 ```
 
-When the build is completed, all the stuff that you need in order to run Milvus will be installed under `[Milvus root path]/core/milvus`.
+When the build is completed, everything that you need in order to run Milvus will be installed under `[Milvus root path]/core/milvus`.
 
 ### Launch Milvus server
 
@@ -141,6 +142,7 @@ To enter the container:
 ```shell
 $ docker exec -it [container_id] bash
 ```
+
 ### Step 3 Download Milvus source code
 
 Download latest Milvus source code:
@@ -195,7 +197,13 @@ Follow the steps below to solve this problem:
 
 ### Error message: `internal compiler error`
 
-Try increasing the memory allocated to docker.
+Try increasing the memory allocated to Docker. If this doesn't work, you can reduce the number of threads in CMake build in `[Milvus root path]/core/build.sh`.
+
+```shell
+make -j 8 install || exit 1 # The default number of threads is 8.
+```
+
+Note: You might also need to configure CMake build for faiss in `[Milvus root path]/core/src/index/thirdparty/faiss`.
 
 ### Error message: `error while loading shared libraries: libmysqlpp.so.3`