adding pplacer install script

docker/install_pplacer.sh

@@ -0,0 +1,32 @@
+#!/bin/bash
+
+bin=/usr/local/bin
+
+# install pplacer and accompanying python scripts
+PPLACER_BUILD=1.1.alpha19
+PPLACER_DIR=pplacer-Linux-v${PPLACER_BUILD}
+PPLACER_ZIP=${PPLACER_DIR}.zip
+PPLACER_GH="https://github.com/matsen/pplacer"
+
+pplacer_is_installed(){
+    $bin/pplacer --version 2> /dev/null | grep -q "$PPLACER_BUILD"
+}
+
+if pplacer_is_installed; then
+    echo -n "pplacer is already installed: "
+    $bin/pplacer --version
+else
+    mkdir -p src && \
+	(cd src && \
+	wget -nc --quiet $PPLACER_GH/releases/download/v$PPLACER_BUILD/$PPLACER_ZIP && \
+	unzip -o $PPLACER_ZIP && \
+	cp $PPLACER_DIR/{pplacer,guppy,rppr} $bin)
+    # confirm that we have installed the requested build
+    if ! pplacer_is_installed; then
+	echo -n "Error: you requested pplacer build $PPLACER_BUILD "
+	echo "but $($venv/bin/pplacer --version) was installed."
+	echo "Try removing src/$PPLACER_ZIP first."
+	exit 1
+    fi
+fi
+