Add docs for googletest

Author: caic99

CMakeLists.txt

@@ -225,7 +225,7 @@ IF (BUILD_TESTING)
   enable_testing()
   find_package(Threads)
   set(CMAKE_CXX_STANDARD_REQUIRED ON)
-  find_package(GTest HINTS /usr/local/lib/ PATHS ${GTEST_DIR})
+  find_package(GTest HINTS /usr/local/lib/ ${GTEST_DIR})
   if(NOT ${GTEST_FOUND})
     include(FetchContent)
     FetchContent_Declare(

doc/install.md

@@ -124,7 +124,7 @@ If Libxc is not installed in standard path (i.e. installed with a custom prefix
 cmake -B build -DLibxc_DIR=~/libxc
 ```
 
-To build tests for abacus, define `BUILD_TESTING` flag.
+To build tests for abacus, define `BUILD_TESTING` flag. You can also specify path to local installation of [Googletest](https://github.com/google/googletest) by setting `GTEST_DIR` flags. If not found in local, the configuration process will try to download it automatically.
 
 ```bash
 cmake -B build -DBUILD_TESTING=1
@@ -139,6 +139,8 @@ cmake --build build -j9
 cmake --install build
 ```
 
+`-j9` specifies the number of jobs to run simultaneously. You can change the number on your need: set to the number of CPU cores to gain the best performance.
+
 [back to top](#download-and-install)
 
 ### Build ABACUS with make