Fix typos in docs

[ci-skip]

docs/source/install.rst

@@ -1,4 +1,4 @@
-installing and upgrading:
+Installing and upgrading:
 ========================= 
 
 You can install pwman3 simply by unpacking the archive and running:

docs/source/packaging.rst

@@ -1,5 +1,5 @@
-Packaging for UNIX\Linux 
-======================== 
+Packaging for UNIX\\Linux 
+========================= 
 
 Requirements and suggested packages
 -----------------------------------