Correct english in README/description

Author: Artyom Abakumov

doc/README.services_extension

@@ -72,7 +72,7 @@ Start user trace session :
 	parameter(s)
 		isc_spb_trc_name     : trace session name, string, optional
 		isc_spb_trc_cfg      : trace session configuration, string, mandatory
-		isc_spb_trc_plugins  : plugins to use for session
+		isc_spb_trc_plugins  : plugins for use with trace session; valid separators: '\t', ',', ';'
 
 	output
 		text message with status of operation :

doc/README.trace_services

@@ -81,7 +81,7 @@ Action parameters switches :
   -N[AME]    <string>                   Session name
   -I[D]      <number>                   Session ID
   -C[ONFIG]  <string>                   Trace configuration file name
-  -P[LUGINS] <string list>              Plugins list to use for trace session
+  -P[LUGINS] <string list>              Plugins list for use with trace session; valid list separators: '\t', ',', ';'
 
 Connection parameters switches :
   -SE[RVICE]  <string>                  Service name

src/include/firebird/impl/msg/fbtracemgr.h

@@ -38,5 +38,5 @@ FB_IMPL_MSG(FBTRACEMGR, 37, trace_switch_user_only, -901, "00", "000", "switch \
 FB_IMPL_MSG(FBTRACEMGR, 38, trace_switch_param_miss, -901, "00", "000", "mandatory parameter \"@1\" for switch \"@2\" is missing")
 FB_IMPL_MSG(FBTRACEMGR, 39, trace_param_act_notcompat, -901, "00", "000", "parameter \"@1\" is incompatible with action \"@2\"")
 FB_IMPL_MSG(FBTRACEMGR, 40, trace_mandatory_switch_miss, -901, "00", "000", "mandatory switch \"@1\" is missing")
-FB_IMPL_MSG_NO_SYMBOL(FBTRACEMGR, 41, "  -P[LUGINS]  <string list>             Plugins list to use for trace session")
+FB_IMPL_MSG_NO_SYMBOL(FBTRACEMGR, 41, "  -P[LUGINS]  <string list>             Plugins list for use with trace session; valid list separators: <tab>, <comma>, <semicolon>")
 FB_IMPL_MSG_NO_SYMBOL(FBTRACEMGR, 42, "  fbtracemgr -SE service_mgr -START -NAME my_trace -CONFIG my_cfg.txt -PLUGINS fbtrace,custom_plugin")