add PropTypes to components

src/components/Layout/Footer.js

@@ -1,4 +1,5 @@
 import React from "react";
+import PropTypes from "prop-types";
 
 import { makeStyles } from "@material-ui/core/styles";
 import { AppBar, Toolbar, Typography, Container } from "@material-ui/core";
@@ -45,4 +46,9 @@ function Footer({ title, lang }) {
   );
 }
 
+Footer.propTypes = {
+  title: PropTypes.string.isRequired,
+  lang: PropTypes.string.isRequired,
+};
+
 export default Footer;

src/components/Layout/Header.js

@@ -1,4 +1,5 @@
 import React, { useState } from "react";
+import PropTypes from "prop-types";
 import routes from "@config/routes";
 
 import { makeStyles } from "@material-ui/core/styles";
@@ -112,4 +113,11 @@ function Header({ twhelpUrl, lang, languages, pathname }) {
   );
 }
 
+Header.propTypes = {
+  lang: PropTypes.string.isRequired,
+  twhelpUrl: PropTypes.string.isRequired,
+  pathname: PropTypes.string.isRequired,
+  languages: PropTypes.arrayOf(PropTypes.string),
+};
+
 export default Header;

src/components/Layout/LanguageSelector.js

@@ -1,4 +1,5 @@
 import React from "react";
+import PropTypes from "prop-types";
 import plFlag from "@images/flags/pl.svg";
 import usaFlag from "@images/flags/usa.svg";
 
@@ -60,4 +61,10 @@ function LanguageSelector({ lang, languages, pathname }) {
   );
 }
 
+Header.propTypes = {
+  lang: PropTypes.string.isRequired,
+  pathname: PropTypes.string.isRequired,
+  languages: PropTypes.arrayOf(PropTypes.string),
+};
+
 export default LanguageSelector;

src/features/CommandsPage/Command.js

@@ -1,4 +1,5 @@
 import React from "react";
+import PropTypes from "prop-types";
 
 import { Card, CardHeader, CardContent, Typography } from "@material-ui/core";
 
@@ -21,4 +22,11 @@ function Command({ command, commandSyntax, description, example }) {
   );
 }
 
+Command.propTypes = {
+  command: PropTypes.string.isRequired,
+  commandSyntax: PropTypes.string.isRequired,
+  description: PropTypes.string.isRequired,
+  example: PropTypes.string.isRequired,
+};
+
 export default Command;

src/pages/404.js

@@ -25,7 +25,11 @@ const NotFoundPage = ({ location, pageContext }) => {
       lang={pageContext.langKey}
       pathname={location.pathname}
     >
-      <SEO title="404: Not found" location={location.pathname} />
+      <SEO
+        title="Page Not found"
+        description="Page not found"
+        location={location.pathname}
+      />
       <Container className={classes.container}>
         <Typography gutterBottom variant="h1">
           Page Not Found