BUG: A read-only DataFrame cannot be .diff()'ed
- [x] I have checked that this issue has not already been reported.

- [x] I have confirmed this bug exists on the latest version of pandas.

- [ ] (optional) I have confirmed this bug exists on the master branch of pandas.

---

**Note**: Please read [this guide](https://matthewrocklin.com/blog/work/2018/02/28/minimal-bug-reports) detailing how to provide the necessary information for us to reproduce your bug.

#### Code Sample, a copy-pastable example

```python
import numpy as np
import pandas as pd

data = np.ones(2, dtype=int)
data.flags.writeable = False
df = pd.DataFrame(data)
df.diff()

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-2-df60a870b020> in <module>
      2 data.flags.writeable = False
      3 df = pd.DataFrame(data)
----> 4 df.diff()

~/miniconda3/envs/dts/lib/python3.8/site-packages/pandas/core/frame.py in diff(self, periods, axis)
   7247             return self.T.diff(periods, axis=0).T
   7248 
-> 7249         new_data = self._mgr.diff(n=periods, axis=bm_axis)
   7250         return self._constructor(new_data)
   7251 

~/miniconda3/envs/dts/lib/python3.8/site-packages/pandas/core/internals/managers.py in diff(self, n, axis)
    546 
    547     def diff(self, n: int, axis: int) -> "BlockManager":
--> 548         return self.apply("diff", n=n, axis=axis)
    549 
    550     def interpolate(self, **kwargs) -> "BlockManager":

~/miniconda3/envs/dts/lib/python3.8/site-packages/pandas/core/internals/managers.py in apply(self, f, align_keys, **kwargs)
    394                 applied = b.apply(f, **kwargs)
    395             else:
--> 396                 applied = getattr(b, f)(**kwargs)
    397             result_blocks = _extend_blocks(applied, result_blocks)
    398 

~/miniconda3/envs/dts/lib/python3.8/site-packages/pandas/core/internals/blocks.py in diff(self, n, axis)
   1265     def diff(self, n: int, axis: int = 1) -> List["Block"]:
   1266         """ return block for the diff of the values """
-> 1267         new_values = algos.diff(self.values, n, axis=axis, stacklevel=7)
   1268         return [self.make_block(values=new_values)]
   1269 

~/miniconda3/envs/dts/lib/python3.8/site-packages/pandas/core/algorithms.py in diff(arr, n, axis, stacklevel)
   1914         # TODO: can diff_2d dtype specialization troubles be fixed by defining
   1915         #  out_arr inside diff_2d?
-> 1916         algos.diff_2d(arr, out_arr, n, axis)
   1917     else:
   1918         # To keep mypy happy, _res_indexer is a list while res_indexer is

pandas/_libs/algos.pyx in pandas._libs.algos.diff_2d()

~/miniconda3/envs/dts/lib/python3.8/site-packages/pandas/_libs/algos.cpython-38-x86_64-linux-gnu.so in View.MemoryView.memoryview_cwrapper()

~/miniconda3/envs/dts/lib/python3.8/site-packages/pandas/_libs/algos.cpython-38-x86_64-linux-gnu.so in View.MemoryView.memoryview.__cinit__()

ValueError: buffer source array is read-only
```

#### Problem description

`df.diff()` does not seem like a data-mutating operation, at least not to me. My read is that `df.iloc[]` was given the same assessment in 2015 (#10043).

#### Expected Output

```
        0
0     nan
1 0.00000
```

#### Output of ``pd.show_versions()``

<details>
```
INSTALLED VERSIONS
------------------
commit           : d9fff2792bf16178d4e450fe7384244e50635733
python           : 3.8.3.final.0
python-bits      : 64
OS               : Linux
OS-release       : 5.4.0-42-generic
Version          : #46-Ubuntu SMP Fri Jul 10 00:24:02 UTC 2020
machine          : x86_64
processor        : x86_64
byteorder        : little
LC_ALL           : None
LANG             : en_HK.UTF-8
LOCALE           : en_HK.UTF-8

pandas           : 1.1.0
numpy            : 1.19.1
pytz             : 2020.1
dateutil         : 2.8.1
pip              : 20.1.1
setuptools       : 49.2.0.post20200714
Cython           : None
pytest           : 6.0.1
hypothesis       : None
sphinx           : None
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : None
html5lib         : None
pymysql          : None
psycopg2         : 2.8.5 (dt dec pq3 ext lo64)
jinja2           : 2.11.2
IPython          : 7.16.1
pandas_datareader: None
bs4              : 4.9.1
bottleneck       : None
fsspec           : None
fastparquet      : None
gcsfs            : None
matplotlib       : 3.2.2
numexpr          : None
odfpy            : None
openpyxl         : None
pandas_gbq       : None
pyarrow          : None
pytables         : None
pyxlsb           : None
s3fs             : None
scipy            : 1.5.0
sqlalchemy       : 1.3.18
tables           : None
tabulate         : 0.8.3
xarray           : None
xlrd             : None
xlwt             : None
numba            : None
```
</details>
