patch: correct and add examples. (#3092)

pages/common/patch.md

@@ -1,16 +1,24 @@
 # patch
 
 > Patch a file (or files) with a diff file.
-> Note that diff files contain both the target filenames and list of changes.
+> Note that diff files should be generated by the `diff` command.
 
-- Apply a patch:
+- Apply a patch using a diff file (filenames must be included in the diff file):
 
-`patch < {{patch_file}}.diff`
+`patch < {{patch.diff}}`
 
-- Apply a patch to current directory:
+- Apply a patch to a specific file:
 
-`patch -p1 < {{patch_file}}.diff`
+`patch {{path/to/file}} < {{patch.diff}}`
+
+- Patch a file writing the result to a different file:
+
+`patch {{path/to/input_file}} -o {{path/to/output_file}} < {{patch.diff}}`
+
+- Apply a patch to the current directory:
+
+`patch -p1 < {{patch.diff}}`
 
 - Apply the reverse of a patch:
 
-`patch -R < {{patch_file}}.diff`
+`patch -R < {{patch.diff}}`