Add help message to README.md

README.md

@@ -27,3 +27,49 @@ Usage
 
 `./bin/rss-cli --help`
 
+Full help message
+
+```
+Usage: ./bin/rss-cli [-u FEED_URI] [CHANNEL FLAGS] [-i ITEM_INDEX] [ITEM FLAGS]
+Options:
+Required Options:
+ [-u, --uri] URI        URI of the rss stream
+
+Channel information:
+ [-t, --title]          Get title of channel
+ [-l, --link]           Get link to channel
+ [-d, --description]    Get description of channel
+ [-e, --language]       Get language code of channel
+ [-m, --webmaster]      Get webMaster's email
+ [-c, --copyright]      Get copyright
+ [-p, --pubdate]        Get publishing date
+ [-q, --managingeditor] Get managing editor
+ [-g, --generator]      Get generator of this feed
+ [-o, --docs]           Get link to RSS documentation
+ [-w, --ttl]            Get ttl, time that channel can be
+                        cached before being updated
+ [-b, --builddate]      Get last time the channel's
+                        content changed
+ [-i, --item] INDEX     Provide index of item to display
+                        If no index is provided, assume the first
+                        item in the feed. All following flags will
+                        be parsed as item options, till another
+                        item is provided
+
+Item options:
+ [-t, --title]          Get title of item
+ [-l, --link]           Get link
+ [-d, --description]    Get description
+ [-a, --author]         Get author
+ [-z, --category]       Get category list
+ [-f, --comments]       Get link to comments
+ [-j, --guid]           Get GUID
+ [-p, --pubdate]        Get publishing date
+ [-s, --source]         Get source of item
+
+General options:
+ [-h, --help]           Show this message
+
+For more information, refer to the RSS 2.0 documentation
+https://validator.w3.org/feed/docs/rss2.html
+```