Apply overwrite help (#323)

* add --apply-overwrites option description to help message
test/overwrite/Makefile: make test-timestamp more flexible for fewer false fails, remove trailing white
* further update help msg

app/builtin/help.c

@@ -55,7 +55,7 @@ static int main_help(int argc, const char *argv[]) {
     "  -0,--header-row <header> : insert the provided CSV as the first row (in position 0)",
     "                             e.g. --header-row 'col1,col2,\"my col 3\"'",
 #ifdef ZSV_EXTRAS
-    "  -1,--apply-overwrites    : automatically apply cached overwrites",
+    "  -1,--apply-overwrites    : automatically apply overwrites saved via `overwrite` command",
 #endif
     "  -v,--verbose             : verbose output",
     "",

app/ext_example/test/expected/zsvext-test-3.out

@@ -32,7 +32,7 @@ Options common to all commands except `prop`, `rm` and `jq`:
   -S,--keep-blank-headers  : disable default behavior of ignoring leading blank rows
   -0,--header-row <header> : insert the provided CSV as the first row (in position 0)
                              e.g. --header-row 'col1,col2,"my col 3"'
-  -1,--apply-overwrites    : automatically apply cached overwrites
+  -1,--apply-overwrites    : automatically apply overwrites saved via `overwrite` command
   -v,--verbose             : verbose output
 
 Commands that parse CSV or other tabular data:
@@ -92,7 +92,7 @@ Options common to all commands except `prop`, `rm` and `jq`:
   -S,--keep-blank-headers  : disable default behavior of ignoring leading blank rows
   -0,--header-row <header> : insert the provided CSV as the first row (in position 0)
                              e.g. --header-row 'col1,col2,"my col 3"'
-  -1,--apply-overwrites    : automatically apply cached overwrites
+  -1,--apply-overwrites    : automatically apply overwrites saved via `overwrite` command
   -v,--verbose             : verbose output
 
 Commands that parse CSV or other tabular data: