unix: Add exit and paste-mode hints to shell startup banner.

Thanks to @nyov for the initial patch.

tests/cmdline/repl_basic.py.exp

@@ -1,4 +1,5 @@
 MicroPython \.\+ version
+Use \.\+
 >>> # basic REPL tests
 >>> print(1)
 1

tests/cmdline/repl_cont.py.exp

@@ -1,4 +1,5 @@
 MicroPython \.\+ version
+Use \.\+
 >>> # check REPL allows to continue input
 >>> 1 \\\\
 ... + 2

tests/cmdline/repl_emacs_keys.py.exp

@@ -1,4 +1,5 @@
 MicroPython \.\+ version
+Use \.\+
 >>> # REPL tests of GNU-ish readline navigation
 >>> # history buffer navigation
 >>> 1

tests/feature_check/repl_emacs_check.py.exp

@@ -1,4 +1,5 @@
 MicroPython \.\+ version
+Use \.\+
 >>> # Check for emacs keys in REPL
 >>> t = \.\+
 >>> t == 2

unix/main.c

@@ -153,7 +153,8 @@ STATIC char *strjoin(const char *s1, int sep_char, const char *s2) {
 #endif
 
 STATIC int do_repl(void) {
-    mp_hal_stdout_tx_str("MicroPython " MICROPY_GIT_TAG " on " MICROPY_BUILD_DATE "; " MICROPY_PY_SYS_PLATFORM " version\n");
+    mp_hal_stdout_tx_str("MicroPython " MICROPY_GIT_TAG " on " MICROPY_BUILD_DATE "; "
+        MICROPY_PY_SYS_PLATFORM " version\nUse CTRL-D to exit, CTRL-E for paste mode\n");
 
     #if MICROPY_USE_READLINE == 1