Small C++ client README tweaks. (#4019)

* Small C++ client README tweaks.

* Followup to review comments.

cpp-client/README.md

@@ -13,11 +13,15 @@ C++ compiler and tool suite (cmake etc).
  sudo apt update
  sudo apt install curl git g++ cmake make build-essential zlib1g-dev libssl-dev
  ```
+
 4. Make a new directory for the Deephaven source code and assign that directory
  to a temporary shell variable. This will make subsequent build steps easier.
  ```
- mkdir -p ~/src/deephaven && cd ~/src/deephaven && export DHSRC=`pwd`
+ export DHSRC=$HOME/src/deephaven
+ mkdir -p $DHSRC
+ cd $DHSRC
  ```
+
 5. Clone deephaven-core sources.
  ```
  cd $DHSRC
@@ -27,9 +31,9 @@ C++ compiler and tool suite (cmake etc).
 6. Build and install dependencies for Deephaven C++ client.
 
  Get the `build-dependencies.sh` script from Deephaven's base images repository
- at `https://github.com/deephaven/deephaven-base-images/blob/main/cpp-client`
+ at https://github.com/deephaven/deephaven-base-images/blob/main/cpp-client
  You can download it directly from the link
- `https://github.com/deephaven/deephaven-base-images/raw/main/cpp-client/build-dependencies.sh`
+ https://github.com/deephaven/deephaven-base-images/raw/main/cpp-client/build-dependencies.sh
  (this script is also used from our automated tools, to generate a docker image to
  support tests runs; that's why it lives in a separate repo).
  The script downloads, builds and installs the dependent libraries
@@ -44,11 +48,13 @@ C++ compiler and tool suite (cmake etc).
 
  Example:
  ```
- mkdir -p $HOME/dhcpp
- cd $HOME/dhcpp
+ # Ensure you have DHCPP defined as above.
+ mkdir -p $DHCPP
+ cd $DHCPP
  wget https://github.com/deephaven/deephaven-base-images/raw/main/cpp-client/build-dependencies.sh
  chmod +x ./build-dependencies.sh
- # Maybe edit build-dependencies.sh to reflect choices of build tools and build target
+ # Maybe edit build-dependencies.sh to reflect choices of build tools and build target;
+ # defaults should work fine for supported platforms.
  ./build-dependencies.sh
  ```
 
@@ -57,10 +63,9 @@ C++ compiler and tool suite (cmake etc).
  ```
  cd $DHSRC/deephaven-core/cpp-client/deephaven/
  mkdir build && cd build
- export DEEPHAVEN_LOCAL=$HOME/dhcpp/local # This should reflect your selection in the previous point.
- export CMAKE_PREFIX_PATH=${DEEPHAVEN_LOCAL}/abseil:${DEEPHAVEN_LOCAL}/boost:${DEEPHAVEN_LOCAL}/cares:${DEEPHAVEN_LOCAL}/flatbuffers:${DEEPHAVEN_LOCAL}/gflags:${DEEPHAVEN_LOCAL}/immer:${DEEPHAVEN_LOCAL}/protobuf:${DEEPHAVEN_LOCAL}/re2:${DEEPHAVEN_LOCAL}/zlib:${DEEPHAVEN_LOCAL}/grpc:${DEEPHAVEN_LOCAL}/arrow:${DEEPHAVEN_LOCAL}/deephaven
- export NCPUS=$(getconf _NPROCESSORS_ONLN)
- cmake -DCMAKE_INSTALL_PREFIX=${DEEPHAVEN_LOCAL}/deephaven .. && make -j$NCPUS install
+ export DHCPP=$HOME/dhcpp # This should reflect your selection in the previous point.
+ source $DHCPP/env.sh
+ cmake -DCMAKE_INSTALL_PREFIX=${DHCPP}/local/deephaven .. && make -j$NCPUS install
  ```
 
 8. Build and run the deephaven example which uses the installed client.