ci: add python 3.10 (#738)

* ci: add python 3.10

see #737

* docs: add version to trigger ci

.github/workflows/cli-test.yml

@@ -17,6 +17,7 @@ jobs:
         python-version:
           - "3.6"
           - "3.8"
+          - "3.10"
     steps:
       - uses: actions/checkout@v2
       - uses: actions/setup-python@v2

cli/README.md

@@ -2,7 +2,7 @@
 
 ## Install
 
-    python3 -m pip install --user lesspass
+    python3 -m pip install --user lesspass # 3.6, 3.8+
 
 ## Usage