docs: Add comments to get-version.sh (#4)

.github/workflows/get-version.sh

@@ -16,7 +16,17 @@
 
 # Pull a tag or version number from versions.txt.
 
+# Get the directory this script is in.
 dir=$(dirname "$0")
+# Get the key we want to look for in versions.txt.
+# This is the first (and only) argument to the script.
 key="$1"
 
+# 1. "cat" will output the text file to stdout.
+# 2. "grep" will filter for a line that begins with the desired key,
+#    and only send matching lines to stdout.
+#    ("^" is the regex character for "beginning of line")
+# 3. "sed" will transform the output of grep by removing everything up to
+#    and including the colon and space characters, leaving only the value
+#    as output to stdout.
 cat "$dir"/versions.txt | grep "^$key:" | sed -e 's/.*: //'