completion: pip: Lint all pip files and clarify comment

completion/available/pip.completion.bash

@@ -1,10 +1,11 @@
+# shellcheck shell=bash
+
 # https://pip.pypa.io/en/stable/user_guide/#command-completion
-# Of course, you should first install the pip, say on Debian:
+# Of course, you should first install pip, say on Debian:
 # sudo apt-get install python-pip
-# sudo apt-get install python3-pip
 # If the pip package is installed within virtual environments, say, python managed by pyenv,
-# you should first initilization the corresponding environment.
-# So that the pip/pip3 is in system's path.
+# you should first initialize the corresponding environment.
+# So that pip is in the system's path.
 if _command_exists pip; then
-    eval "$(pip completion --bash)"
+	eval "$(pip completion --bash)"
 fi

completion/available/pip3.completion.bash

@@ -1,10 +1,11 @@
+# shellcheck shell=bash
+
 # https://pip.pypa.io/en/stable/user_guide/#command-completion
-# Of course, you should first install the pip, say on Debian:
-# sudo apt-get install python-pip
+# Of course, you should first install pip, say on Debian:
 # sudo apt-get install python3-pip
 # If the pip package is installed within virtual environments, say, python managed by pyenv,
-# you should first initilization the corresponding environment.
-# So that the pip/pip3 is in system's path.
+# you should first initialize the corresponding environment.
+# So that pip3 is in the system's path.
 if _command_exists pip3; then
-    eval "$(pip3 completion --bash)"
+	eval "$(pip3 completion --bash)"
 fi

completion/available/pipenv.completion.bash

@@ -1,4 +1,4 @@
-if _command_exists pipenv
-then
-    eval "$(pipenv --completion)"
+# shellcheck shell=bash
+if _command_exists pipenv; then
+	eval "$(pipenv --completion)"
 fi