docs: Use a better input example in the streaming section (#3322)

The introduction says all the usage examples (e.g. of truncate_stream,
etc) in the section use [0,[1]] as input, but they actually use [1,[2]].
["a",["b"]] seems better than [1,[2]] as the string values won't be
confusable with the indexes in <path>.

docs/content/manual/dev/manual.yml

@@ -3384,8 +3384,8 @@ sections:
 
       Several builtins are provided to make handling streams easier.
 
-      The examples below use the streamed form of `[0,[1]]`, which is
-      `[[0],0],[[1,0],1],[[1,0]],[[1]]`.
+      The examples below use the streamed form of `["a",["b"]]`, which is
+      `[[0],"a"],[[1,0],"b"],[[1,0]],[[1]]`.
 
       Streaming forms include `[<path>, <leaf-value>]` (to indicate any
       scalar value, empty array, or empty object), and `[<path>]` (to
@@ -3402,9 +3402,9 @@ sections:
           given streaming expression.
 
         examples:
-          - program: 'truncate_stream([[0],1],[[1,0],2],[[1,0]],[[1]])'
+          - program: 'truncate_stream([[0],"a"],[[1,0],"b"],[[1,0]],[[1]])'
             input: '1'
-            output: ['[[0],2]', '[[0]]']
+            output: ['[[0],"b"]', '[[0]]']
 
       - title: "`fromstream(stream_expression)`"
         body: |
@@ -3413,9 +3413,9 @@ sections:
           outputs.
 
         examples:
-          - program: 'fromstream(1|truncate_stream([[0],1],[[1,0],2],[[1,0]],[[1]]))'
+          - program: 'fromstream(1|truncate_stream([[0],"a"],[[1,0],"b"],[[1,0]],[[1]]))'
             input: 'null'
-            output: ['[2]']
+            output: ['["b"]']
 
       - title: "`tostream`"
         body: |