Created SC2285 (markdown)

SC2285.md

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+## Remove spaces around += to assign (or quote '+=' if literal).
+
+### Problematic code:
+
+```sh
+var += "my text"
+```
+
+### Correct code:
+
+```sh
+var+="my text"
+```
+
+### Rationale:
+
+ShellCheck found an unquoted `+=` after a word. To append text to a variable, remove spaces around `+=` as in the example.
+
+### Exceptions:
+
+If the `+=` was supposed to be literal, you can quote it to make ShellCheck ignore it:
+
+    grep '+=' files..
+
+### Related resources:
+
+* Help by adding links to BashFAQ, StackOverflow, man pages, POSIX, etc!