Ignore lines that don't start with pipe in Mkdwn

Only parse lines that start with a pipe for the Markdown table source.

README.md

@@ -129,8 +129,7 @@ following format:
 * Use a BEGIN and END comment tag surrounding the table block in a Markdown
   document. These begin/end comment strings are configurable.
 
-* Ensure each row of the table begins with a pipe (`|`). It doesn't have to
-  have one at the end.
+* Only lines that begin with a pipe (`|`) are parsed.
 
 * The header names are irrelevant.
 
@@ -143,10 +142,11 @@ following format:
 
 * The table column headers are customizable.
 
-* The list of tags may optionally be formatted (e.g. with single backticks,
-  italics, bold) and can be a comma-separated list of tags with wildcards.
+* The tag column may be a single tag or a list of comma-separated tags. The
+  values can optionally be surrounded in backticks and can use wildcards.
 
-* The deletion date format is customizable. Set the [date format](#date-format).
+* The date column should be a single date value in the configured
+  [date format](#date-format).
 
 ## Running
 
@@ -176,10 +176,14 @@ Basic usage:
         markdown_file: README.md
 ```
 
-__NOTE:__ You __must__ explicitly set one or both of `json_file` and
-`markdown_file` for anything to happen.
+* The GitHub Action exposes all of the [environment
+  variables](#environment-variables) as action inputs. At a minimum, the
+  `dockerhub_username`, `dockerhub_password`, and `dockerhub_repository` must
+  be set in addition to `markdown_file` and/or `json_file`.
 
-Setting custom configuration, showing all action inputs:
+* Use `v1` for the action version for now.
+
+An example showing all inputs:
 
 ```yaml
     - name: Docker Hub Tag Deleter

hub-tag-delete.py

@@ -89,13 +89,14 @@ def get_readme_table():
     for line in md_file:
         if line.startswith(config['markdown']['begin_string']):
             parsing = True
-        if parsing and not line_is_ignored(line):
-            # ignore empty lines
-            if line.strip():
-                linenum += 1
-                # Skip the header and separator (first two lines)
-                if linenum > 2:
-                    items.append(parse_md_line(line))
+        if parsing:
+            if line.startswith('|') and not line_is_ignored(line):
+                # ignore empty lines
+                if line.strip():
+                    linenum += 1
+                    # Skip the header and separator (first two lines)
+                    if linenum > 2:
+                        items.append(parse_md_line(line))
         if line.startswith(config['markdown']['end_string']):
             parsing = False