### What problem does this PR solve?
Add `.doc` file parser, using tika.
```
pip install tika
```
```
from tika import parser
from io import BytesIO
def extract_text_from_doc_bytes(doc_bytes):
file_like_object = BytesIO(doc_bytes)
parsed = parser.from_buffer(file_like_object)
return parsed["content"]
```
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
---------
Co-authored-by: chrysanthemum-boy <fannc@qq.com>
parse markdown files as txt
### What problem does this PR solve?
support markdown files
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
### What problem does this PR solve?
_Briefly describe what this PR aims to solve. Include background context
that will help reviewers understand the purpose of the PR._
Issue link:#[[Link the issue
here](https://github.com/infiniflow/ragflow/issues/236)]
### Type of change
- [x] Documentation Update
### What problem does this PR solve?
_Briefly describe what this PR aims to solve. Include background context
that will help reviewers understand the purpose of the PR._
Issue link:#[[Link the issue
here](https://github.com/infiniflow/ragflow/issues/226)]
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
