update build doc with protobuf libs

howto_compile.md

@@ -5,6 +5,7 @@ LMDB
 ----
 
 This lib is necessary for all executables. Let your distribution do the job.
+(liblmdb-dev on debian).
 
 osmpbf
 ------
@@ -12,6 +13,9 @@ osmpbf
 This lib is necessary only for the creation of route database. Do not do this in
 the rv2 dir but in the dir which contains rv2 (or change rv2 src makefile).
 
+This lib need libprotobuf to be build and the protobuf compiler. Let your
+distribution do the job (libprotobuf-dev and protobuf-compiler on debian).
+
 {{{
     git clone https://github.com/inphos42/osmpbf.git
     cd osmpbf