(DOC) A `string` passed to `groupby` is hard to understand based on current doc

Code Sample, a copy-pastable example if possible

From Here

For DataFrame objects, a string indicating a column to be used to group. Of course 
df.groupby('A') is just syntactic sugar for df.groupby(df['A']), but 
it makes life simpler
For DataFrame objects, a string indicating an index level to be used to group.

Problem description

These two sentences are in a kind of conflict with each other, until one read until she read the note below.

Expected Output

Reword to make it clear that a string may indicate column or index level

Output of pd.show_versions()

INSTALLED VERSIONS ------------------ commit: None python: 3.5.3.final.0 python-bits: 64 OS: Darwin OS-release: 16.6.0 machine: x86_64 processor: i386 byteorder: little LC_ALL: None LANG: en_US.UTF-8 LOCALE: en_US.UTF-8

pandas: 0.21.0.dev+193.gb2b5dc32e pytest: 3.1.2 pip: 9.0.1 setuptools: 36.0.1 Cython: 0.25.2 numpy: 1.13.0 scipy: 0.19.0 xarray: None IPython: 6.0.0 sphinx: 1.6.2 patsy: 0.4.1 dateutil: 2.6.0 pytz: 2017.2 blosc: None bottleneck: 1.2.1 tables: None numexpr: 2.6.2 feather: None matplotlib: 2.0.2 openpyxl: None xlrd: None xlwt: None xlsxwriter: None lxml: None bs4: None html5lib: 0.9999999 sqlalchemy: None pymysql: None psycopg2: None jinja2: 2.9.6 s3fs: None pandas_gbq: None pandas_datareader: None

[sanchiprakash]

is this still open? i would like to proceed with it.

[Nikhil1O1]

I submitted a pull request with the issue concerned above. #36238 @jreback @BranYang