Strip trailing whitespace from prose in top-level and package READMEs

Three stray single trailing spaces at end of prose lines:

- README.md (Security Considerations section):
  * end of the 'MarkItDown performs I/O...' paragraph
  * end of the 'Sanitize your inputs:' paragraph
- packages/markitdown/README.md:
  * end of the [!TIP] callout description line

Some Markdown renderers (and Markdown Lint / Prettier / etc.) treat a
trailing double-space as an explicit line break, so accidental single
trailing spaces show up as diff noise on every unrelated edit. They
also make grep/regex line-ends less reliable.

Prose-only change, no rendering impact intended.

Proposed by community PR #1838 (only the whitespace part; that PR
also unrelated changes that blocked it from merging).

Author: chienyuanchang

README.md

@@ -341,9 +341,9 @@ You can help by looking at issues or helping review PRs. Any issue or PR is welc
 
 ### Security Considerations
 
-MarkItDown performs I/O with the privileges of the current process. Like `open()` or `requests.get()`, it will access resources that the process itself can access. 
+MarkItDown performs I/O with the privileges of the current process. Like `open()` or `requests.get()`, it will access resources that the process itself can access.
 
-**Sanitize your inputs:** Do not pass untrusted input directly to MarkItDown. If any part of the input may be controlled by an untrusted user or system, such as in hosted or server-side applications, it must be validated and restricted before calling MarkItDown. Depending on your environment, this may include restricting file paths, limiting URI schemes and network destinations, and blocking access to private, loopback, link-local, or metadata-service addresses. 
+**Sanitize your inputs:** Do not pass untrusted input directly to MarkItDown. If any part of the input may be controlled by an untrusted user or system, such as in hosted or server-side applications, it must be validated and restricted before calling MarkItDown. Depending on your environment, this may include restricting file paths, limiting URI schemes and network destinations, and blocking access to private, loopback, link-local, or metadata-service addresses.
 
 **Call only the conversion method you need:** Prefer the narrowest conversion API that fits your use case. MarkItDown's `convert()` method is intentionally permissive and can handle local files, remote URIs, and byte streams. If your application only needs to read local files, call `convert_local()` instead. If you need more control over URI fetching, call `requests.get()` yourself and pass the response object to `convert_response()`. For maximum control, open a stream to the input you want converted and call `convert_stream()`.
 

packages/markitdown/README.md

@@ -1,7 +1,7 @@
 # MarkItDown
 
 > [!TIP]
-> MarkItDown is a Python package and command-line utility for converting various files to Markdown (e.g., for indexing, text analysis, etc). 
+> MarkItDown is a Python package and command-line utility for converting various files to Markdown (e.g., for indexing, text analysis, etc).
 >
 > For more information, and full documentation, see the project [README.md](https://github.com/microsoft/markitdown) on GitHub.