update documentation for simdjson submodule

Change-Id: I9a3f9a33dd4f2e6fcb06e9c35146f14bf61c914d

Author: rdementi

README.md

@@ -55,6 +55,18 @@ And finally a daemon that stores core, memory and QPI counters in shared memory
 Building PCM Tools
 --------------------------------------------------------------------------------
 
+Clone PCM repository with submodules:
+
+```
+git clone --recursive https://github.com/opcm/pcm.git
+```
+
+or clone the repository first, and then update submodules with:
+
+```
+git submodule update --init --recursive
+```
+
 Install cmake then:
 
 ```

doc/PCM_RAW_README.md

@@ -38,7 +38,11 @@ pcm-raw -e core/config=0x00000000004300c5,name=BR_MISP_RETIRED.ALL_BRANCHES -e c
 Collecting Events By Names From Event Lists (https://download.01.org/perfmon/)
 --------------------------------------------------------------------------------
 
-pcm-raw can also automatically lookup the events from the json event lists (https://download.01.org/perfmon/) and translate them to raw encodings itself. To make this work you need to download simdjson library in the PCM source directory and recompile PCM:
+pcm-raw can also automatically lookup the events from the json event lists (https://download.01.org/perfmon/) and translate them to raw encodings itself. To make this work you need to checkout PCM with simdjson submodule:
+
+* use git clone --recursive flag when cloning pcm repository, or
+* update submodule with command `git submodule update --init --recursive`, or
+* download simdjson library in the PCM source directory and recompile PCM:
 
 1. change to PCM 'src/' directory
 2. git clone https://github.com/simdjson/simdjson.git

src/CMakeLists.txt

@@ -113,7 +113,9 @@ if(SIMDJSON_IS_APPLICABLE)
         else()
             message(WARNING
                 " ${CMAKE_CURRENT_SOURCE_DIR}/simdjson/singleheader/simdjson.h doesn't exist\n"
-                " Run 'git clone https://github.com/simdjson/simdjson.git' in 'src' directory to get simdjson library")
+                " Use `git clone --recursive` flag when cloning pcm repository to clone simdjson submodule as well or\n"
+                " update submodule with command 'git submodule update --init --recursive' or\n"
+                " run 'git clone https://github.com/simdjson/simdjson.git' in 'src' directory to get simdjson library")
         endif()
     endif(simdjson_FOUND)
 endif(SIMDJSON_IS_APPLICABLE)