docs: improve some docstrings in utils

Author: Rogdham

CHANGELOG.md

@@ -24,6 +24,10 @@ adheres to [Semantic Versioning](https://semver.org/).
   tradeoff defaulting to keeping the last 8 LZMA decompressors used
 - Typing: use `BinaryIO` instead of `IO[bytes]`
 
+### :house: Internal
+
+- Minor improvements in some docstrings
+
 ## [0.3.1] - 2021-12-26
 
 [0.3.1]: https://github.com/rogdham/python-xz/releases/tag/v0.3.1

src/xz/utils.py

@@ -19,7 +19,6 @@ class FloorDict(_MutableMapping[int, T]):
     Differences from dict:
      - keys must be int
      - obj[key] will return the value whose key is the closest one which is lower or equal to key
-     - obj[key, True] will return the real index of the value in the form (index, obj[key])
     """
 
     def __init__(self) -> None:
@@ -114,7 +113,7 @@ class Foo:
 
     If attribute is "a" and proxy is "b", it proxies to ".a.b".
 
-    If the proxy is None, then use a local value instead,
+    If the proxy value is None, then use a local value instead,
     which acts as a temporary storage in the meanwhile.
     """