Fix typos

runtime/tutor

@@ -1546,7 +1546,7 @@ letters! that is not good grammar. you can fix this.
  each active selection. Similarly, the :append-output appends a
  shell command output after each active selection.
 
- Go the next line starting with -->, move to the space
+ Go to the next line starting with -->, move to the space
  character at the end of the line, and enter
      :append-output date
  to append the date at the end of the line.
@@ -1599,14 +1599,14 @@ letters! that is not good grammar. you can fix this.
 =================================================================
 
  * Shell commands can be run from helix, showing output in a
- popup, with :sh .
+ popup, with :sh.
 
  * Shell commands can be run from helix and their output inserted
  (resp. appended) using :insert-output (resp :append-output),
- also aliased as ! (resp Alt-!)
+ also aliased as ! (resp Alt-!).
 
- * Selections can be piped to a shell command and their output 
+ * Selections can be piped to a shell command and the output 
- can overwrite the commmand (resp. be discarded) using :pipe
+ can overwrite the selection (resp. be discarded) using :pipe
  (resp. :pipe-to), also aliased as | (resp. Alt-| ). Remember
  that this is piping the selection(s) as the pipe operator would
  do in bash, not providing the data as arguments.