Update indexing.rst

Adding a warning, and example, about using attribute access to create a new column.
BUG: lookup global constants correctly in query/eval
Merge pull request #7181 from cpcloud/eval-with-inf

BUG: correctly lookup global constants in query/eval
Merge pull request #7188 from AllenDowney/patch-1

Update indexing.rst
BUG: bug in recognizing out-of-bounds positional list indexer with iloc and a multi-axis tuple indexer (GH7189)
Merge pull request #7189 from jreback/panel_iloc

BUG: bug in recognizing out-of-bounds on iloc indexers on tuple indexers (GH )
DOC: fix api doc build warning
BUG: Bug in setitem with a single item, and a multi-index and integer indicies (GH7190)
Merge pull request #7191 from jreback/loc_bug

BUG: Bug in setitem with a single item, and a multi-index and integer indices (GH7190)