Add Joining Lines Together as a vim til.

vim/joining-lines-together.md

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+# Joining Lines Together
+
+You can quickly join a series of lines onto a single line using the `J`
+command. Simply hitting 'J' in normal mode will join the current line with
+the line below it leaving a space in between the two. If you want to join
+the next 5 lines, you can hit `5J`. Hitting '5J' on this:
+
+```
+first,
+second,
+third,
+fourth,
+fifth
+```
+
+will transform it into this:
+
+```
+first, second, third, fourth, fifth
+```
+
+Similarly, you can perform a line by line join on a visual selection by
+hitting `J` after making the desired visual selection.