Update 'BUILD.md'

BUILD.md

@@ -1,5 +1,15 @@
+# Marsey instructions
+Run the script: ./marsey/marsey_replacer.sh
+
+Then follow the build instructions for CBDT.
+
+Despite the instructions stating it would take about 3 minutes, it took about 30 minutes on my computer. Use this snippet to track progress:
+
+`echo "$(( 100 * $(ls build/compressed_pngs|wc -l) / $(ls build/quantized_pngs |wc -l) ))"'%'` 
 # Build instructions
 
+--- 
+
 Typically build the CBDT then the COLRv1 as COLRv1 copies some information from CBDT.
 
 ## CBDT
@@ -34,4 +44,4 @@ python colrv1_postproc.py
 
 ## Emojicompat
 
-TODO detailed instructions
+TODO detailed instructions