"Let's" → "lets". (#295)

Third-person singular simple present form of "let" is obviously intended, judging from grammatical context.
Contraction of "let us" is erroneously used instead.

Author: Erquint

README.md

@@ -126,7 +126,7 @@ jobs:
             LICENSE
 ```
 
-> **⚠️ Note:** Notice the `|` in the yaml syntax above ☝️. That let's you effectively declare a multi-line yaml string. You can learn more about multi-line yaml syntax [here](https://yaml-multiline.info)
+> **⚠️ Note:** Notice the `|` in the yaml syntax above ☝️. That lets you effectively declare a multi-line yaml string. You can learn more about multi-line yaml syntax [here](https://yaml-multiline.info)
 
 > **⚠️ Note for Windows:** Paths must use `/` as a separator, not `\`, as `\` is used to escape characters with special meaning in the pattern; for example, instead of specifying `D:\Foo.txt`, you must specify `D:/Foo.txt`. If you're using PowerShell, you can do this with `$Path = $Path -replace '\\','/'`